Smoothing a rough casting

[dominick]

  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? 

grymster,  At the time I wrote this, I didn't know what size barrel he had. Chucking a mortar barrel with trunnions and spinning it would not be a good idea anyway.  I bought a 10" x 18" wood lathe for smoothing barrels and it works very well.  I never liked grinding and sanding on my metal lathe because of all of the grinding dust over the bed ways and slides.  With the wood lathe the grinding dust doesn't matter and with a barrel between the centers, the carriage is not there in the way.

[Terry C.]

... 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?  

From what I understand, one of the issues with vent erosion in bronze guns was that the hot jet of flame would leach out the tin from the bronze.

I don't imagine lead would fare well. Copper would be a better choice. Copper was the material of choice for vent liners in the old days.

FWIW, the angles don't have to be a perfect match.

[KABAR2]

Why not bore your vent on the other side?
Since the dimple would be on the bottom it wouldn't be seen
or if it bothers you fill it with Bondo it will be hid with black paint.

Why not use a stainless bolt for the vent? stainless is rust resistant very hard
and I doubt you would ever wear it out firing.

[little seacoast]

Kabar, it's the dimple at the bottom of the drilled vent hole caused by the point of the drill that I was concerned about.  The outside dimple isn't an issue.  I have used a SS bolt for the vent liner, its bottom is flat and does not conform to the contour of the hole bottom which is a shallow V.  The lead "washer" is intended to fill this gap and the point of junction between the casting and liner, if it erodes I'll just replace it.  Like I said, this is an experiment on my part, maybe a copper seal next time.
 
Terry C, It's good to know that less than perfect surface mating will do, I'll have to try your suggestion with a copper rod.  If it looks good enough I'll drill out the lead seal and give it a try. I used your sketch from a previous thread as my blueprint.

[partsproduction]

     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.
Tracy & Mike

 I've fashioned a vacuum intake close to the tool before, makes a ton of difference in air quality in the shop, if it's done just so the amount of cast iron grit on the lathe is minimal.

[little seacoast]

Finally finished the Coehorn as much as it ever will be. Please go easy- it's not meant to be 100% authentic, just fun to shoot. Since it's 2.25" ammo is abundant and dirt cheap it should get a lot of use if my back is up to the job.  190 grains of F gives a dependable 100 yards with very little spread.

[Zulu]

That looks like great fun!  I wish I had a place where I could shoot something like that.  Nice job!
Zulu

[dan610324]

aint texas big enough for a 100 yard shooting 
and no need for a back stop either 

[Zulu]

Dan,
There's no doubt Texas is big enough.  When you enter Texas on Interstate 10 from Louisiana, the first sign you see is a milage sign that says "El Paso 787 miles"!
I live in a metropolitan area and don't know anyone in the country where I could shoot.
I live my life through everyone else's adventures.
Zulu

Actually, now that I think about it, the sign says 878 miles, not 787.

[Double D]

Texas gets very defensive when you point out there is no public  access land in Texas...it's not true.  There is public  access land, few and far between and access limited.

[Cat Whisperer]

...
I live in a metropolitan area and don't know anyone in the country where I could shoot.
...

You simply need to practice the art of asking.

Drive to a place a few 10's of miles out, maybe further.

A place not so populated, some place with a gas station, maybe a bar or at least a small general store.

We did that when we went PD hunting in S.D. and needed a place to shoot them.

We started at the local sale barn, Sunday morning - no sale then, but lot of folks there eating breakfast.  A dozen conversations and 4 or 5 phone calls later we were shooting!

[Zulu]

Cat,
That drive would be closer to 1 hour.  There are certainly places an hour away that could allow a place to shoot.  There are even some hills.
Zulu

[dominick]

You did a nice job smoothing the barrel.  Also, you can put a point on the vent liner by chucking the liner in a drill and while it's spinning grind a point on it with a disc sander.  You want the angle slightly sharper so the inner most point is in contact with the barrel [Bottom of vent hole].  Coat the vent liner point with grease it check the fit.  If the grease is touching even then you're good to go.

[VA Rifleman]

Very Nice!!!  I like those patented streamers you shoot.  Now for a camera with a parachute   

[Frank46]

Get thee to a local junkyard and check out the copper bins. You should be able to find some copper flashing as used on roofs and gutters. You could use a wood dowel to form the flashing into a seal (repose') Like they did on the Statue of Liberty. Or find some old copper coins and do the same thing. Frank

[little seacoast]

OMG a Kewpie!

[Zulu]

OMG a Kewpie!

It deserves one.  Nice job!
Zulu

[Cannoneer]

You did good work LS! How much does the whole rig weigh?

[little seacoast]

BoomJ, the mortar and base weigh in @ 145 lbs which is why I use a two wheel hand truck to move it out back for shooting. While I can pick it up and walk off with it, we ain't goin far. It's hell to get old and wimpy.
Thanks for the compliments guys, it was fun to make.

[Cannoneer]

LS,
To my way of thinking that’s right around the poundage where a guy that’s getting his equipment to the range by his lonesome, just might start to think of the needle on the enjoyment meter as pointing more towards the work side than the fun side.
I can just imagine what some of the gents that shoot the big stuff would have to say about that comment: “What a slacker!”
Hey, what can I say, I like living in a well defined comfort zone; yeah, I know that’s just a roundabout way of saying that I’m a little lazy.

[little seacoast]

I hear you about mobility, but my mortar range starts 40 ft behind the shop where the mortar lives and extends 600 yards due west or 150yds north. It's really not bad with the dolly at all.