Author Topic: Smoothing a rough casting (Read 2991 times)

little seacoast · « **on:** April 23, 2010, 02:10:28 PM »

Can anyone do a simple tutorial on how to smooth a casting of iron? I do not have access to a large lathe so this will have to be done with hand tools like an angle grinder and files. The casting isn't real rough, it's not very smooth either.
Any practical help is very welcome. Thanks, LS

dan610324 · « **Reply #1 on:** April 23, 2010, 02:35:35 PM »

an angle grinder is very very difficult to use on an cylindrical object if its not rotating
it will easily be a lot of flat surfaces instead of something round
that will look even vorse then a rough casting

how bad is the casting surface now ?? please show some photos
how perfect do you want it ?? and why ??

how many hours are you prepared to put into this ??
how large is the barrel ??

best result would you probably get with long strips of emery cloth
and a hundred hours or so with hard labour

but please explain a little more
what do you have
and what do you want

Zulu · « **Reply #2 on:** April 23, 2010, 03:07:53 PM »

A hundred hours of hard labor is not hard to imagine. You will get out of this what you put into it.
What are you looking for? Post some pictures.
Zulu

GGaskill · « **Reply #3 on:** April 23, 2010, 03:48:33 PM »

After you give us some pictures and a description of where you want to end up, I will add more, but for starters, fill any cavities with Bondo. Then I would start with a coarse file and draw file the worst roughness, keeping in mind you want to do the whole surface rather than work in one place. Otherwise you will get a divit where you spend too much time.

Then get some of the rolls of abrasive cloth in a coarse grit and work over the whole surface shoe shine style with lengths that give good strokes. Go to finer grades of abrasive to get a smoother finish. Use a block around the trunnions, rimbases, etc.

I can't imagine having to go finer than 120 unless you are looking for shine.

dominick · « **Reply #4 on:** April 23, 2010, 06:29:17 PM »

You could use a wood lathe depending on the size and weight of the barrel. A used one can sometimes be picked up cheap or possibly one like Harbor Freight sells. All you need to do is rotate the barrel while sanding. Here's A link to one. http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=34706

KABAR2 · « **Reply #5 on:** April 23, 2010, 07:14:22 PM »

If the casting is smooth like a Napoleon with no moldings that would be lost,
with care you could use an automotive disc sander with a soft rubber backer
the trick is to keep it moving and it would be good to have a rudimentary fixture
to hold it so you can turn it, it would help having some experience with a sander
to cut down the learning curve.

little seacoast · « **Reply #6 on:** April 24, 2010, 05:54:25 AM »

OK, a few pictures. This is a Hern 24lb Coehorn casting and no rougher than their pictures show.

I have thought that I would like it a little smoother, not shiny smooth though. If the originals were this rough I'll just leave as is. I do have a large old Yates American wood lathe that I could mount it on but the RPM may be a little high.
At 90 lbs I wouldn't like to have it get away from me!

dan610324 · « **Reply #7 on:** April 24, 2010, 06:26:32 AM »

both the copy and the originals was cast in sand molds , so I guess the result would be the same
but maybe they put a lot of labour on it after the casting on the originals
at least I know that they did on the bronze cannons

Soot · « **Reply #8 on:** April 24, 2010, 07:13:30 AM »

A high build primer would fill all that in, just strip the old finish off first.

Cannoneer · « **Reply #9 on:** April 24, 2010, 09:25:27 AM »

LS,
The major reason that Britain (and others) transitioned so quickly in the latter 1700's to iron naval guns was because of cost, so when iron founding technology had developed to a point where the guns were deemed more dependable, the switch from bronze to iron was underway. Any reliable history that you read is going to relate how these guns were utilitarian in nature, they weren't meant to impress with their surface finish, a greater amount of time and money given to the manufacture of the gun's bores made more sense.
Even by the time of our Civil War, while the North had the manufacturing capabilities to machine even the largest Rodman exteriors to a smooth finish, the South didn't have that luxury, so it was decided by their leadership that Tredegar, Bellona, Selma, and other foundries were going to leave the exteriors of their cast iron Brooke rifles and smoothbores, Columbiads, siege mortars, etc., in a fairly rough state, and concentrate their energies on increasing the quantity produced.

Zulu · « **Reply #10 on:** April 24, 2010, 10:40:17 AM »

On the other hand, everyone likes a well finished gun.

Zulu

seacoastartillery · « **Reply #11 on:** April 24, 2010, 10:52:34 AM »

   We are currently faced with a similar task here at Seacoast Artillery Company. A friend gave us a 2/3 scale 6 pdr., maker unknown. The finish is, in a word, terrible, i.e., rough as a cob. We thought about turning it, but we really don't want that abrasive cast iron dust all over our lathe, so it's files or body grinders. Abrasive hand grinders are great for many items, but cannon tubes aren't one of them unless you rotate the tube slowly to avoid dwell time in any one area. We have chosen to mount our tube on an engine stand fitted with a sturdy pipe so the tube can be rotated by hand so as to present new surfaces for filing. We figure 5 course and three medium files will be necessary to complete this job, about 40 dollars worth. In short, we are doing this lob exactly as foundry workers through the ages did it, the slow, but effective way.

   If you want to see the tools and tooling used in the old days you can click on this link:

   http://www.gboreloaded.com/forums/index.php/topic,160153.60.html
Tracy & Mike

Rough as a cob, field artillery tube and our only smoothing tool.

Even the cascabel needs work, one BIG void and roughness on knob.

You can see here what tool the foundry workers at West Point Foundry used on this original 100 Pdr. Parrott Rifle, Model 1861.

At F.P.F. the foundry workers used the same technique on the band between the trunnions where lathe tools could not go.

Terry C. · « **Reply #12 on:** April 24, 2010, 12:12:19 PM »

If you plan to use an angle grinder, don't use the grinding disc.

Get a flap disc (we call them blenders). These are built up from overlapping tiles of abrasive cloth, glued to a rigid backing. While the edges of the flaps are new with sharp corners, work on the worst spots and stay out in the open away from any radius. As the corners of the flaps round off, you can start to work into harder to reach areas without damaging the casting.

Lowes has them, but I get mine at a local industrial shop supplies dealer for less. Shop around.

Oh, by the way: Always 'pull' a new sharp disc across the work, never 'push' it or the sharp corners of the flaps could dig in. After the corners have started to fray and round off, you can work in either direction.

little seacoast · « **Reply #13 on:** April 24, 2010, 02:11:23 PM »

Thanks for all the good advice guys. After seeing your 6 pdr Mike and Terry I will have to revise my description to just a little rough. I think that I will pursue this with a combination of the means suggested-
Mount the casting vertically on a slow turntable
Remove the worst of the "rough" with a combinarion of files and the flap sander
discs
Spend some hours with abrasive strips of various grades to maybe 100
Paint with a high build primer ( any specific brands?)
I will try to post a few pictures as the work progresses

Soot · « **Reply #14 on:** April 24, 2010, 02:24:49 PM »

Quote

Paint with a high build primer ( any specific brands?)

I don't remember the brand I used to use. It was an epoxy primer that you could paint over with any type of paint.
It would build up so high that you could fill a #10 screw hole with it, more like spray bondo.

RocklockI · « **Reply #15 on:** April 24, 2010, 03:27:01 PM »

The 13 inch mortar at the Denver Nature Museum has a better finish than that .

Cannoneer · « **Reply #16 on:** April 24, 2010, 06:46:09 PM »

Quote from: Zulu on April 24, 2010, 10:40:17 AM

On the other hand, everyone likes a well finished gun.
Zulu

Zulu,
You're preaching to the choir, I may have an even bigger Jones for finely honed finishes than you do,

but the man did say: If the originals were this rough I'll just leave as is.
I would even agree 100% with your statement, if for the sake of realism, you'd change "everyone likes" to 'many people like'.

In all seriousness, (or at least with a little more seriousness) I think that there are more than a few members here who aren't all that concerned with having a finely finished piece, but are perfectly content to just have a safe tube to burn some powder in.
Now, if John A. Dahlgren shouldn't be considered a perfectionist, then I don't know who should, and even he didn't think it necessary that the rear third of his huge 15-inchers be brought to a smooth finish. It would seem that in this instance practicality won out over aesthetics; why waste labor and time when the effort wasn't going to improve the functionality of the gun?

Double D · « **Reply #17 on:** April 24, 2010, 07:34:02 PM »

Something to keep in mind about fine finishes on military guns, extra work cost extra money. Budgets even back then were tight. Money would be spent on function, not finish.

GGaskill · « **Reply #18 on:** April 24, 2010, 08:10:59 PM »

While I don't know how applicable it would be in these circumstances, a polished finish is sometimes stronger than a rough finish because the roughness actually acts like cracks in the surface where fatigue cracks will start. Polishing the cracks out lessens the stress points that would otherwise be there.

grymster · « **Reply #19 on:** April 25, 2010, 02:42:25 PM »

Quote from: dominick on April 23, 2010, 06:29:17 PM

You could use a wood lathe depending on the size and weight of the barrel. A used one can sometimes be picked up cheap or possibly one like Harbor Freight sells. All you need to do is rotate the barrel while sanding. Here's A link to one. http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=34706

I dunno.... 90 lbs turning at 600 RPM on a lathe that weighs something less than 180 lbs?

GGaskill · « **Reply #20 on:** April 25, 2010, 02:47:31 PM »

You wouldn't need 600 rpm if you were using a flap sander.

grymster · « **Reply #21 on:** April 26, 2010, 07:14:45 AM »

Quote from: GGaskill on April 25, 2010, 02:47:31 PM

You wouldn't need 600 rpm if you were using a flap sander.

That's minimum spindle speed on the linked lathe.

a4beltfed2000 · « **Reply #22 on:** April 26, 2010, 11:34:24 AM »

SeacoastArty-

Can you post a pick of how you are working that 2/3 scale barrel? just hand turning and filing?

thanks for any info!

Littleseacoast-

On the picture is shows a semi circle recession? is that for the fuse vent hole? What are the deminisions on the Hern piece? overall length-diameter? trunnions? does it have a vent hole or liner? does the barrel have a steel liner? what is the bore diameter?

little seacoast · « **Reply #23 on:** April 27, 2010, 02:18:51 AM »

All the specs are on the Hern web site in the stickies I think. It is 2.25" bore and does have a substantial steel liner. The dimple is the site for the fuse hole and I am debating a vent liner now. By the time I've smoothed it down some- 50 hours or so from now- I will have made up my mind. To ease the ammo situation I'm trying to standardize on just a few cailbers, this will go with Dom's Parrott I hope (no comparison intended).

Double D · « **Reply #24 on:** April 27, 2010, 04:02:03 AM »

Quote from: little seacoast on April 27, 2010, 02:18:51 AM

All the specs are on the Hern web site in the stickies I think. It is 2.25" bore and does have a substantial steel liner. The dimple is the site for the fuse hole and I am debating a vent liner now. By the time I've smoothed it down some- 50 hours or so from now- I will have made up my mind. To ease the ammo situation I'm trying to standardize on just a few cailbers, this will go with Dom's Parrott I hope (no comparison intended).

Whats to debate. It is a lined barrel, the intersection of the liner and casting is a point of corrosion, and has a history of failure. It is a safety issue, line the vent. It may never fail in your lifetime, but when your grandson fires it, it could fail and injure or kill you great grandson.

dan610324 · « **Reply #25 on:** April 27, 2010, 09:13:12 AM »

yeah its always better to be safe than sorry

seacoastartillery · « **Reply #26 on:** April 27, 2010, 10:08:32 AM »

a4beltfed2000, We don't have any more pics, but bet that you know how to hold a file anyway. We might use one of Terry C.'s bonded flap wheels in the old angle grinder just as a finish blend, staying away from sharp edges or radii like he suggested. Filing will clean up 95% of it and files are infinitely more controllable when your truing up the edge of the rimbases and other critical areas like that. Keep those grinders away from the muzzle or it will look like a baboon butt, not too pretty! You might need some Bondo here and there; the professional cannon tube manufacturers use it on a rough castings to fill in pits before painting, so why shouldn't you? Use it very sparingly, however, only after all filing and grinding has been finished. Make darn sure it is thoroughly cured and rock-hard before sanding. Good luck.

Mike and Tracy

1Southpaw · « **Reply #27 on:** April 29, 2010, 09:52:12 AM »

I think my Power pipe threader head would be the right speed . It's a Ridgid tool about 60 years , old turns slow . Never measured the RPM.

little seacoast · « **Reply #28 on:** May 08, 2010, 02:20:02 PM »

DD, it's not a question of whether or not so much as how. It is still a choice however.
GGaskill has kindly provided me with a few hints on drilling and tapping cast iron that I got to try today with results that went far better than I dreamed possible.
One remaining little detail has me in an quandry however. There is no way in hell that I can bevel the insert bolt to exactly the angle of the drill bit used to drill the vent hole. I have decided to try an end run around this by using a slug of soft lead (half an egg sinker 1/2" diameter) as a compressable gasket to seal the bolt end/ liner interface. Anybody see any problem with this solution?

Cat Whisperer · « **Reply #29 on:** May 08, 2010, 02:48:11 PM »

Quote from: little seacoast on May 08, 2010, 02:20:02 PM

...
I have decided to try an end run around this by using a slug of soft lead (half an egg sinker 1/2" diameter) as a compressable gasket to seal the bolt end/ liner interface. Anybody see any problem with this solution?

In steamfitting GORTEX is often used for formable gaskets. Lead may or may not work. The copper disk on the end of the breechplug on my .50 cal cannon compressed and leaked over time; I would think that lead would do the same.

Included angle on drill bits is commonly 118 degrees (59 each side). You could come very close by spinning the vent liner in a drill press and use a file.