Author Topic: Trunnion Pockets on a Drill Press  (Read 4374 times)

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Offline GGaskill

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Trunnion Pockets on a Drill Press
« on: November 28, 2008, 07:30:27 PM »
Someone posted a request earlier today for a method of making trunnion pockets on a drill press with emphasis on getting them truly opposite each other.  The post seems to have disappeared (at least I can't find it anymore) but here goes anyway.



This is basically my setup.  Now obviously it is on a milling machine, not a drill press, but bear with me.  There are two important features about this setup for locating trunnion pockets.  First, the barrel is held between centers so it is perpendicular to the spindle.  Second, it is held in an indexing device to allow it to be rotated exactly 180°.  You will note the generous use of short pieces of 2x4 and bar clamps.  These are there to add clamping power to the lathe dog and indexer to prevent rotation of the barrel while the machining is going on.

Now let's transpose this setup onto a drill press (dp).  Since the dp doesn't have an adjustable table (and the adjustable tables that can be had for dp's aren't very rigid so I don't recommend using them for this), we will need to mount the holding devices to something that can be slid around on the dp table to align the barrel with the spindle.  I would get a adequately long piece of 2x6 that is both straight and flat and a couple of pieces of 4x6 at least 6" long (these dimensions are assuming a barrel of  about 4" maximum diameter; a smaller one could use a smaller jig.)  One piece will hold your dead center, the other an adjustable (for length) center.  They need to be drilled through for 8" long 3/8" lag bolts.  The holes need to be the same distance from one edge, say 4.5", and of sufficient diameter that the threads on the bolts will be engaged.  It would be a good idea to put 60° points on the threaded ends of bolts to the minor diameter of the threads.  Glue and screw one piece of 4x6 with lag screw to one end of the 2x6.  The other piece needs to be located such that the barrel will fit between it and the previously anchored one.  I would generously apply drywall screws but no glue as you may want to use this on barrels of differing length.  Make sure the screw points are at the same height from the bottom of the 2x6; if they aren't, shim the second piece of 4x6 (or sand it thinner) until they are.  If you don't, the trunnions will not be perpendicular to the bore.

The other issue is to get the pockets on truly opposite sides of the barrel.  Presuming you have welding capability, I would lightly weld a piece of 1/2x1" steel about 4" long to the barrel in a place that can be easily repaired when you take this piece off.  Assuming the barrel at this time has no features that require a particular orientation of the trunnions, it doesn't matter where the 4" piece is located.  We are going to use it as a reference plane and the trunnions are going to be located parallel to it.  The barrel will be located be applying a square to the 4" piece such that it is perpendicular to the table and parallel to the spindle.  Securely clamp the barrel in position on the jig to prevent rotation.  Measure the diameter of the barrel at the center of the trunnions.  Divide this number by two.  The following part of the procedure requires more than two hands.  Place a square on the upper flat of the jig against the side of the barrel at the trunnnion centerline and measure from the square the radius of the barrel as above determined. Put an accurately located center punch mark there.  Using a wiggler in the dp chuck, center the center punch mark under the spindle and clamp the jig to the dp table securely.  (I'm not much of a wiggler user myself; I think you will have to put the wiggler in the punch mark with the spindle turned off, then raise the spindle and turn on the machine at low RPM looking for the wiggler to be swinging around.  You need to move the jigged barrel such that the wiggler doesn't move after it is lifted.)

You are now ready to drill.  It is a good idea to set the depth stop so you don't accidentally drill into the bore.  After you have drilled the first pocket, loosen the anti-rotation clamps and rotate the barrel, aligning it with the square on the opposite side.  Apply the clamps again and drill the other pocket.

Now, having written all of that, I think you need to remember that the pockets need to be flat bottomed and a twist drill has a 118° point.  So you should regrind your drill to a flat bottom and redrill after roughing out most of the material with a regular drill.  This is going to cause some extra vibration as the drill is not now set up to remove metal efficiently, so be careful.

After you have finished the pockets, remove the welded on piece and clean up the spots where the welds were.

It would be possible to make a jig using V-blocks instead of centers but that requires calculations and accurately made/measured V-blocks  (because of the usual taper of a barrel) to get the bore horizontal.
GG
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Offline KABAR2

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Re: Trunnion Pockets on a Drill Press
« Reply #1 on: November 28, 2008, 07:57:27 PM »
That is a nicely turned barrel! If someone has a milling machine it would be the way to go as it is a rock solid base compared to a drill press.

Something to consider when using a drill press for this type of operation I have seen drill chucks unseat with certain harmonics set up by chatter with larger bits,

you mention regrinding a drill bit but what about using an endmill of the correct size.... more flutes less chatter.
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Offline Victor3

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Re: Trunnion Pockets on a Drill Press
« Reply #2 on: November 29, 2008, 01:33:05 AM »
 Excellent ideas.

 A quick & dirty method I've used for such things on occasion...

 1. Drill 1st hole on location by whatever method you choose (this is the easy part).

 2. Get (or make) a pin to perfectly fit the hole diameter.

 3. Fix the pin parallel (straight up & down) to the DP spindle in a V-block/vise arrangement, or wood/metal block by glueing or welding it in place.

 4. Using an indicator held in the DP chuck, indicate the pin diameter concentric with the DP spindle, then clamp/bolt the pin-holding assembly to the table.

 5. Set the barrel onto the pin, locating it in the 1st trunnion hole (taking care not to move the pin).

 6. Support and clamp the barrel on both ends by whatever method is convenient.

 7. Drill 2nd hole. If all goes well, it should be concentric to the 1st hole.
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Offline accuratemike

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Re: Trunnion Pockets on a Drill Press
« Reply #3 on: November 29, 2008, 03:51:39 AM »
When I did mine, I used the first trunion to locate the second. I made sure the first trunion was true and had a FLAT end, and was pressed in straight. I left the jigging on the table, so the second would be in the same location relative to the barrel. Then I flipped the barrel over and pushed it down against the flat end of the first trunion. This should have put me 180° out for the second hole, it worked. I also roughed the hole with an end mill and the bored to achieve proper press. To get this in one step, you would have to turn the trunion to match the final size of a hole made with the end mill. There are probably alot of work-arounds for this, I have no indexer. MIKE

Offline Josco

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Re: Trunnion Pockets on a Drill Press
« Reply #4 on: November 29, 2008, 11:11:46 AM »
I started with hex material and laid out my trunion pocket locations and bored to the proper depth with a 1/2" endmill on my small P&W milling  machine prior to turning. Locations came out within a few thousands.

Offline Josco

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Re: Trunnion Pockets on a Drill Press
« Reply #5 on: November 29, 2008, 11:14:45 AM »
Hex material on my miller.


Offline GGaskill

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Re: Trunnion Pockets on a Drill Press
« Reply #6 on: November 29, 2008, 01:40:34 PM »
I can see no problem using a center cutting end mill to drill the pockets if you can find one that is the correct size.  Drills come in a greater assortment of sizes.  Personally, I tend to cheat on trunnion diameters so I can use standard tooling.

All the other ways proposed here are OK too but the theme in this thread was using a drill press for those who don't have a milling machine.  If you have a mill, use of a boring head allows you to make scale trunnions/rimbases since you can adjust the diameter to whatever it takes.

I would like to add an additional comment to the original text.  The procedure described expects that you have not yet drilled the bore in the barrel.  If you have, you will need to make a tight fitting muzzle plug with a center hole in the external face to support the barrel bewteen centers.  I am also assuming that you have a center hole in the cascable (it can be welded up once it is no longer needed.)
GG
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Offline seacoastartillery

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Re: Trunnion Pockets on a Drill Press
« Reply #7 on: November 29, 2008, 03:06:27 PM »
     Thanks for posting this topic and your well thought out method, George.  Mike and I figured that your post would bring out other methods as well.  Ours, that we used in the Nano Mortar thread, was strictly designed for micro or nano cannon and had no adjustment features at all.  Yours is far more practical for the size cannon that most folks want to build.  We are also glad to see that we are not the only machinists in this world who like to have their tools "at hand" where they can actually be used.   Great looking tube!

Regards,

Tracy and Mike
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Offline Double D

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Re: Trunnion Pockets on a Drill Press
« Reply #8 on: November 29, 2008, 03:09:36 PM »
Here's how I did my first ones on the drill press.  First I computed the location and finish depth of my trunnion pocket.

Then I faced of the end of my unturned stock.  I painted the end with dykem.  Then with my combination square as a guide, I scribed a line across the end and then another about 90 degrees to the first.  I put the round stock on the drill press braced it with dunnage and loosely clamped it with clamps. I then measured from the center intersection of the scribed line on the end to the floor.  I adjusted the table height a little to get an even mark, then I rolled the round until each end of one of the scribed lines was the same measurement as the intersection.    I then drilled my holes with series progressively larger drill bits untill I had the trunnion pocket to depth and diameter I wanted. My Trunnions were made from William Greens plans  with a threaded shank and threaded hole in the bottom of the pocket. At that time I did not know how to use a mill so the trunnion pocket bottom was the same included angle as the drill bit. I also made my trunnions bottom to this same angle.

After one pocket was in I rolled the stock 180 degrees and realigned everything using the scribed line.  

For turning, I made some false trunnions and screwed them in the pockets.  I put the stock in the lathe and cutting away from the head stock trimmed the false trunnions down to same diameter of the round stock.  After this I turned my profile working towards the head stock.  

After the gun was fully profiled, I put the turned gun back in the drill press and drilled a hole towards the outer edge of the breech end of the false trunnion.  Using a punch at an angle in the hole I was able to unscrew the false trunnions and then screw in my real trunnion using loctite and a barrel wrench to set them.  

The next semester I learned how to use the mill and index.  The first set of trunnion pockets I did with the index were about 170 degrees...don't ask how, that was 25 years ago.  That barrel is sitting over in corner.  Bad pockets have been  filled and welded with false trunnions and new 180 degrees trunnion in place.  I should finish that gun some day.

Offline Josco

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Re: Trunnion Pockets on a Drill Press
« Reply #9 on: November 30, 2008, 06:10:29 AM »
The purpose of my post showing how I used hex stock for my tube was to show that by starting with hex or square stock it's very easy to locate and scribe the cross hairs for the trunnion pocket locations and they can be drilled
on a drill press with reasonable care if a mill is not available. If you are going to use a drill press, scribe your crosshairs then center punch them accurately, you can feel the intersection of the lines with a sharp center punch then tap lightly and inspect your mark. If all looks good then center punch them deeply. Start with a 60 degree center drill and drill your cone.
Drill finished size with a 135 degree drill, I dub my drills slightly on the front face to reduce the hook angle, this helps prevent chatter,and reduces the chances of the drill grabbing and pulling in. It also will break up the chips and reduces the long stringy chips. After drilling I would go in with another drill of the same size with either a flat bottom or a very slight point of 1 or 2 degrees and finish the flat bottom. By using hex or square stock it's very easy to clamp your work to the mill or drill press table.

  Regards

 Joe Scope

Offline accuratemike

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Re: Trunnion Pockets on a Drill Press
« Reply #10 on: November 30, 2008, 07:03:56 AM »
I can't trust endmills to make holes close enough, if I am looking for a certain press fit. Sure, you can get a hole that a piece of stock can be welded into, but I was looking for .0015-.002" press. I have checked the actual sizes machined by some of my endmills and came up with this: 1 1/2" shell mill cuts +.009", 3/8" 2-flute .373", 3/4" 2-flute .753", 3/4" 4-flute .747", 3/4" ball-end .735", 3/4" roughing .748", 3/4" 4-flute (non center-cutting) .722", 1 1/8" 6-flute .128", and so on. Some are cheap, some are name brand American (didn't seem to matter). I have a chunk of stock that I used all of these in, and then stamped the mill and it's actual size into. I refer back to it when I am looking for a fit. I'll turn or mill the mating part to match the size that I'll end up with. It all is for naught in the long run. After use they dull (a little) and get smaller. I'm sure drills are no better (probably far worse).

There was a discussion recently, on one of the mill boards I follow, about using chucks (and, I guess similarly, drill presses) to drill holes with endmills. The general concensus was, that as long as you were not milling (no side loads) it is feasable. After all, chatter is largely a function of the machine's rigidity. I've seen drill presses many times the size of my mill. I know people use boring heads on drill presses to bore aluminum throttle bodies. With a sufficient machine, anything is possible. Finish and accuracy may or may not suffer. When all I had was a drill press, I misused and abused it to no end. I eventually bucked up for a mill. Things certainly go faster anyhow (without all of the bodging around). I did turn out some serviceable (even nice) stuff though. I wouldn't rule anything out, without trying it, (at least in scrap).

Oh, and BTW, I did make a couple of suitably sized V-blocks to jig my mortar for the trunions. I used my CNC torch and heavy plate. I cleaned up the important faces on the mill. Since then, they have come in handy for other projects. When Dom poo-poohed the torch machine, because his treatise on torching was aimed at what could be done in a little shop with the tools at hand, I neglected to respond that, I made my torch machine in my little shop (with the tools at hand). Sometimes it doesn't hurt to take your craftiness to the next level.

Don't sell yourself (or your tools) short. Anything is possible. just look at what our forefathers had for "tools at hand", and some of the stuff they created. MIKE

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I can see no problem using a center cutting end mill to drill the pockets if you can find one that is the correct size.  Drills come in a greater assortment of sizes.  Personally, I tend to cheat on trunnion diameters so I can use standard tooling.




Offline Cannoneer

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Re: Trunnion Pockets on a Drill Press
« Reply #11 on: December 02, 2008, 01:51:09 AM »
Quote
Someone posted a request earlier today for a method of making trunnion pockets on a drill press with emphasis on getting them truly opposite each other.  The post seems to have disappeared (at least I can't find it anymore) but here goes anyway.

GG, I didn't make the original post, but I was going to ask for advice in the future, right now I've got a couple other projects to finish.
The barrel I have was cast then machined, it is 10.5-inches long, a .50 cal. bore has been drilled 3.5-inches deep (I put a tight fitting dowel in the bore and it seems to be drilled straight) and it only has a shallow centered divit left on the cascabel, but I can drill a deeper hole, and a drill press is all that I have to work with. There has been some good information already posted on this topic, but if anyone has any other suggestions they would be appreciated (keeping in mind a drill press is all that there is to accomplish the task).



RIP John. While on vacation July 4th 2013 in northern Wisconsin, he was ATVing with family and pulled ahead of everyone and took off at break-neck speed without a helmet. He lost control.....hit a tree....and the tree won.  He died instantly.

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Offline GGaskill

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Re: Trunnion Pockets on a Drill Press
« Reply #12 on: December 02, 2008, 12:03:33 PM »
Boom J,
    It is not clear to me what you would like to do.  Drill the bore deeper?  Drill for trunnions?  Something else?  Let me know what you want to do and I will try to give good advice.
GG
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Offline Cannoneer

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Re: Trunnion Pockets on a Drill Press
« Reply #13 on: December 03, 2008, 06:17:07 PM »
Boom J,
    It is not clear to me what you would like to do.  Drill the bore deeper?  Drill for trunnions?  Something else?  Let me know what you want to do and I will try to give good advice.

George,
 I need to do both; finish drilling the bore and drill pockets for the trunnions. The barrel is brass, and I'd like to braze the trunnions in place.
RIP John. While on vacation July 4th 2013 in northern Wisconsin, he was ATVing with family and pulled ahead of everyone and took off at break-neck speed without a helmet. He lost control.....hit a tree....and the tree won.  He died instantly.

The one thing that you can almost always rely on research leading to, is more research.

Offline GGaskill

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Re: Trunnion Pockets on a Drill Press
« Reply #14 on: December 04, 2008, 11:22:39 AM »
Holding the barrel vertically to deepen the bore is going to be more of a challenge than drilling for trunnions.  But since you already have some bore to act as a guide, aligning it, at least, will not be too difficult.  You should be able to align it by simply putting a 1/2" drill in the chuck and running the bore up around it (assuming that it is still a close fit.)

If that works, try this idea.  Build a wooden box (screws only since you will need to take it apart) about the length of the barrel but leave one end open and make the other end larger than the box enough that you can clamp it to the drill press table.  Seal the box inside and out with shellac or some other paint-like material.  Put the barrel on the drill in the drill press and put the box around the barrel.  Mix up enough plaster of paris to fill the box with the barrel in it and pour it into the box.  The theory here is that the plaster will set and hold the barrel in alignment with the drill.  Check to see that the drill comes out freely before proceeding. 

After the plaster has set and cooled off (it gets hot while it is setting), see if the barrel is held tightly enough to prevent rotation; if so, try to drill the rest of the bore.  Make sure you have measured how much deeper you need to drill before plastering the barrel (measure twice, cut once.)  Clear the chips frequently.  Once you have reached target depth, remove the box from the plaster and carefully break the plaster off the barrel.  I don't know how easily the plaster will come off the brass; you may want to test that before immersing the whole barrel.
GG
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Offline Cannoneer

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Re: Trunnion Pockets on a Drill Press
« Reply #15 on: December 05, 2008, 09:32:08 AM »
Holding the barrel vertically to deepen the bore is going to be more of a challenge than drilling for trunnions.  But since you already have some bore to act as a guide, aligning it, at least, will not be too difficult.  You should be able to align it by simply putting a 1/2" drill in the chuck and running the bore up around it (assuming that it is still a close fit.)

If that works, try this idea.  Build a wooden box (screws only since you will need to take it apart) about the length of the barrel but leave one end open and make the other end larger than the box enough that you can clamp it to the drill press table.  Seal the box inside and out with shellac or some other paint-like material.  Put the barrel on the drill in the drill press and put the box around the barrel.  Mix up enough plaster of paris to fill the box with the barrel in it and pour it into the box.  The theory here is that the plaster will set and hold the barrel in alignment with the drill.  Check to see that the drill comes out freely before proceeding. 

After the plaster has set and cooled off (it gets hot while it is setting), see if the barrel is held tightly enough to prevent rotation; if so, try to drill the rest of the bore.  Make sure you have measured how much deeper you need to drill before plastering the barrel (measure twice, cut once.)  Clear the chips frequently.  Once you have reached target depth, remove the box from the plaster and carefully break the plaster off the barrel.  I don't know how easily the plaster will come off the brass; you may want to test that before immersing the whole barrel.

OK GG, I owe you for this one; I've been thinking of some kind of wooden jig set-up, but I couldnt figure out how to make it both straight and sturdy enough to hold the barrel aligned under the drill. I think your concept is going work fine, the only thing I'm going to change is the plaster medium, (my wife has about fifteen/twenty pounds of artists modelling clay that can be made pretty pliable by adding water to it) I've seen video of founders hammering the plaster off of lost wax castings, I think I'll try and avoid that hassle. I'll make the base out of 1/2'' plywood and the walls out of 3/8th, attach them together with drywall screws and seal the inside with Flecto Varathane clear plastic finish. I've had a 1/2'' extended length (12'') high speed twist drill that I got for this task still sitting in the package for awhile now, and I've got the screws, now all I've got to get is the plywood. When I get the box made I'll position the barrel on the bit and move the box clamped to the drill press base up to surround the barrel, then I'll tamp down the clay around the barrel inside the box ( I think this will air dry solid enough to hold the barrel steady while I drill). I will use my shop-vac with a clear plastic gas syphon tube attached to suck the oil and shavings out of the barrel when the bit is lifted. When I'm done drilling, and take the box apart, applying water to the hardened clay should soften it up again and I'll be able to peel it off the barrel. When I get going on this project I'll take some pics of the process. THANKS.
RIP John. While on vacation July 4th 2013 in northern Wisconsin, he was ATVing with family and pulled ahead of everyone and took off at break-neck speed without a helmet. He lost control.....hit a tree....and the tree won.  He died instantly.

The one thing that you can almost always rely on research leading to, is more research.

Offline GGaskill

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Re: Trunnion Pockets on a Drill Press
« Reply #16 on: December 05, 2008, 10:38:49 AM »
I'm not really a clay guy but I do know it hardens by the water evaporating from it so there will need to be some way for the water to escape from the wet clay in the box.  Plaster hardens by a chemical reaction between the water and the plaster so it doesn't need to evaporate.

I am concerned that the clay will take a long time to dry out and it will shrink and move around during the process.  Your call as it's your barrel.

One more idea--after you have drilled the bore to maximum depth with the half inch drill, if there is a step where the old bore meets the new bore, you might consider drilling or reaming the whole thing to 33/64" diameter to get a full length smooth bore.
GG
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Offline dan610324

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Re: Trunnion Pockets on a Drill Press
« Reply #17 on: December 05, 2008, 12:17:27 PM »
I would also guess the clay will shrink during the drying process .

I cant understand when you "have seen them hammering off the plaster" , but there are 2 ways to do the lost wax castings , either you use ceramic shells or you use an good investment to produce an thick mold .

Ive also seen videos where they use pneumatic chissels and sand blasting to clean up the castings .
but thats when they used the ceramic shell method . thats why its called CERAMIC shell .
during the burnout process you heat the ceramic to the shells are almost yellow , then when they cooled down after the casting in fact it is ceramic .

when you use an good quality investment to produce your mold you heat it to 725 degrees celsius during the burnout process , then it depend on size and shape of both mold and the piece you are going to cast what mold temperature you should have during the pour .

but 400 degrees celsius is an good recomendation to start experimenting with . to hot mold and the bronze stay liquid to long and accumulates gases from the mold and being full of gas blisters .
to cold mold and it doesnt fill it up perfect in all angles and patterns .

when I think the bronze have cooled enough to not be liquid any more I throw the mold in the creek I got 5 meters from my garage door .

when the running water cool down the mold it does at the same time take away the investment from the casting , the water floating from the mold is completely white as milk .
5 min later its just the stainless steel flask and the casting left .

the casting is completely clean , maybe I need to use an toothbrush and some water in a few corners .

but this is with an high quality investment from an english company called srs , and after the heating both during the burnout process and the casting , the bronze temperature is 1050  +/- 5   degrees celsius during the pouring .

I would recomend you to test with an piece of scrap rod and dip it in plaster of paris and try to get the plaster away the day after to see how hard it is .
I dont know for sure but I believe its the heating of the investment that makes it so easy to clean from the castings .
Dan Pettersson
a swedish cannon maniac
interested in early bronze guns

better safe than sorry

Offline GGaskill

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Re: Trunnion Pockets on a Drill Press
« Reply #18 on: December 05, 2008, 02:00:44 PM »
Yes, the high temperature heating of the plaster investment reverses the chemical process that occurs when the plaster sets and causes a loss of strength.  In my suggested scenario, the plaster wouldn't be heated so it would still have substantial strength.  However, it could be heated, I suppose, when you want the plaster to break down.

Since your barrel is round, it is going to need some bonding to prevent its rotation when being drilled.  Otherwise, it will turn in the jig which won't be a good thing.
GG
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Offline dan610324

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Re: Trunnion Pockets on a Drill Press
« Reply #19 on: December 05, 2008, 02:37:13 PM »
wouldnt it be easier to just use an machine vise, doesnt need to be any fancy expensive vise .
try to borrow an vise if you dont have one , then use lead plates to protect the barrel .
just align it with the drill in the bore and then fastened it in the vise .
wouldnt be that difficult , but be extremely sensitive wheen feeding the drill downwards .
just take it slow and easy, maybe fill the barrel often with oil .
Dan Pettersson
a swedish cannon maniac
interested in early bronze guns

better safe than sorry

Offline Josco

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Re: Trunnion Pockets on a Drill Press
« Reply #20 on: December 05, 2008, 04:32:44 PM »
After drilling you can polish the bore with a simply built slotted mandrel and emory cloth. I slotted a 3/8" round brass rod about 2" deep with a hacksaw
then 1 wrap of emory cloth. You can mount the mandrel in your drill press
or electric drill and progress with finer emory cloth for a mirror finish.

Offline Cannoneer

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Re: Trunnion Pockets on a Drill Press
« Reply #21 on: December 06, 2008, 09:49:23 AM »
 GG and Dan, I'm not sure that the modelling clay is going to display shrinkage to the extent that you both think it will, but George, I'll be the first to concede that there's no question that the plaster will do a better job of holding the barrel fast. That's my concern, that the plaster is really going to hold to the barrel; Dan, I don't have to conduct an experiment to see how plaster of paris sticks to surfaces, we used some not  long ago to make repairs to wallboard that was damaged by removing wallpaper when remodelling a bathroom, and believe me when it 's allowed to dry on a surface (steel, plastic, wood, fiberboard etc.) it's not easy to get off. If I get the time I'm going to conduct a couple of experiments today; I've got some plaster of paris left and some carriage bolts, so I'm going to cover the smooth part of the bolts with the plaster and let them dry thoroughly, and then use a propane torch to heat one to see if this affects the ease of removal of the plaster, while on the other bolt I'm going to put it in a pot of boiling water to see if this breaks down the plaster. If either of these methods work, then I'm going to use the p of p to do the job. There is also no question that the process of pouring the plaster in the box would to be a lot easier task to achieve than trying to get the clay packed tightly into the form.
Dan, I have a vise that came with the drill press, thats the first thing I tried; maybe it would work for a straight tube but this barrel is already tapered and has the astragals and fillets cut, the vise isn't going to be able to hold the barrel steady enough to drill it, so I'm going with GG's idea, I think his suggestion is the best way to go.
George, I forgot to put this in the earlier post, but I've got a 10-inch long HSS .510 reamer that my neighbor (retired tool and die maker) gave me for this project. Josco, that is a good idea you came up with to bring the bore to a smooth polished finish. Thanks, everyone.
RIP John. While on vacation July 4th 2013 in northern Wisconsin, he was ATVing with family and pulled ahead of everyone and took off at break-neck speed without a helmet. He lost control.....hit a tree....and the tree won.  He died instantly.

The one thing that you can almost always rely on research leading to, is more research.