Turning small brass

[Don Case]

I'm taking a shot at making my own guns. I'm making 10 four pounders. If I figured it right they are 1.75" long and taper from .175 to .11. Any tips for turning brass that small? I seem to remember from high school 60 years ago that the cutting tool should scrape more than cut and maybe the speed should be higher than steel. How about tool height?

Any tips at all. Thanks

[Bob Cleek]

Zero to negative back rake on brass. Google is your friend. There's tons of tutorials on YouTube. Check out "Mr. Pete 222" or "Tubal Cain" on YouTube. He's a retired shop teacher who's got tons of videos on machining on YouTube. They're great!

 

You may want to print something like this out and keep it for reference: http://www.steves-workshop.co.uk/tips/toolgrinding/tool-grinding-poster.pdf

 

 

[Don Case]

Thanks Bob. I did look but I must have put in the wrong parameters. I thought "turning small brass" would do it but all I got was turning brass on a wood lathe.  The internet and I used to get along but lately, not so much. I'll take a peek at those sites.

[TBlack]

Don,

What's the diameter of the rod? And the scale?  I'm assuming you have a lathe, and that you've incorporated the various rings, etc. in the profile?

Tom 

Edited April 4, 2021 by TBlack

[CPDDET]

I assume your using a lathe. Wood or metal lathe? Brand?

I have a Sherline lathe and could be of some assistance if your using that.

I set the cutting edge of the tool even with the center of the piece I'm turning. Speed & feed are determined by the material being turned.

Your lathe manufacturer should be of help with your questions.

[Don Case]

It's a Shoptask lathe/mill. I bought it new in 1990. I'm using .2 dia brass. 1:48 scale. I've done a bit of fiddling with tool height by putting feeler gauges under the tool. I think I've got it working OK now. Very little chatter and a nice finish. I'm using a 1/16" cutoff tool with no rake. Getting the rings to scale is tough. I'm toying with the idea of turning a smooth taper and then wrapping and soldering a very thin copper wire around it for the rings. That may be just as cumbersome.

[dvm27]

Making perfect repeatable  cannons on the lathe can be a bit challenging. Some folks make a form tool for the reinforcements (rings), some use CNC  and some use a lathe duplicator after turning a master in wood. Here is a series from Jo Pi on You Tube on turning a brass cannon that may be of help. He is a master machinist though and his techniques may be a bit above many of our capabilities. 

https://www.youtube.com/watch?v=6i4rffLUqyY&ab_channel=JoePieczynski

[wefalck]

Does your not have a top-slide ? Turning the whole carriage with the crank at the bed on the right seems to be rather cumbersome and it seems difficult to crank, keep an eye on dial readings and watch what happens. How do you turn the taper without top-slide ?

 

Most of my turning of such things is done with a knife-tool that I grind from a HSS-bit. For such dimensions the width at the front should equal or be less then the shortest between two rings. The most used tool has a width of only 0.4 mm at the front and clearance on three sides. In this way I can turn to the left and the right without changing the tool.

I normally make myself a dimensioned sketch and then decide on zero points for movements in both, x- and y-direction. I then note down in the sketch how much I need to move the carriage between the rings, taking into consideration also the width of the tool at the front. In order to avoid backlash issues, all the turning is done in one direction only. In this way I avoid measuring on the workpiece (at least for duplicates). With such a procedure you can turn out identical pieces within the accuracy limits of your machine.

 

If the rings on the cannon need to be rounded, there are two options: you can use either a file to do that or using a forming tool in a secondary operation. As you don't seem to have a QCTP, chaning tools might not be such a good option though.

[thibaultron]

Using a live center at the tailstock would help, as you could use less pressure holding that end of the rod.

 

For repeatability, you could make a flat sheet pattern, put a pointer on the topslide, and mount the pattern to the bed. Then slowly run the dails holding the pionter against the pattern, as you cut the rod.

[Don Case]

No I don't have a top slide. I'm looking for one as it would make it much easier. One of the problems is that i only have to make 10 guns. A compound slide is about $100 for a cheap one. That's $10 a gun. Now if I was making 100 guns🙂. My glue dried so i haven't worked on this for a few days. I keep thinking that there should be a way. I could turn a taper between centers by using a dog and off centering my tailstock. I'll keep this on a back burner for a while til I come up with a solution. The size of the lathe is a problem too. Everything seems to get in the way.

[thibaultron]

You will find the topslide useful for many future projects.

[wefalck]

I would agree with Ron and wonder, why there was no top-silde in the first place. I have seen such combination machines by different makers/vendors and they normally have one. You would need it for short taper turning and finer work.

 

Having said that, I would consider saving up for a small lathe, such as the smallest PROXXON for instance, for really small work, rather than buying a top-slide, which is probably a third or a quarter of the cost of the PROXXON. It may be worthwhile to scan the secondhand market too.

Edited April 5, 2021 by wefalck

[druxey]

Have you considered turning just a master pattern and casting the guns that you need? That way they would all be identical. As Wefalck points out, your lathe set-up is far from ideal for repetitive miniature work.

[allanyed]

You beat me to it Druxey.   I agree with you completely.

 

Don, it is far easier making one perfect barrel and casting as many as you need for your build.  You can cast in metal or casting resin.   Silicone molding material is readily available and far easier than using plaster or some other materials and there is no need to make lost wax castings with all the paraphernalia that is required.    There are some tricks you can use so there is no need to make two piece molds which invariably leave a seam that has to be filed and sanded off.  Making the monogram and vent field are projects in themselves so making these once is an advantage as well. If you decide to go this route feel free to PM me and I can send you information on making your barrels with a single piece mold. 

  

[Bob Cleek]

28 minutes ago, druxey said:

Have you considered turning just a master pattern and casting the guns that you need? That way they would all be identical. As Wefalck points out, your lathe set-up is far from ideal for repetitive miniature work.

Given the tedious repetitive nature of the work and the need for uniformity, without a pattern-tracing device or a custom cutter to turn an entire cannon at one go, I'd also cast my vote for casting any number of cannon that may be required. A low melting point white metal can be used, or casting resins. Another option is electroforming. Remember those copper-coated baby shoes that were popular in the 1940's and 50's? (Yeah, I realize you probably don't.) Basically, you can take anything, such as  a cast wax cannon, spray it with a conductive paint, like that zinc-heavy spray paint they sell to prevent rust or India ink and graphite, and then electroplate it with copper to a thickness you desire. The wax can then be melted by throwing the plated piece in a pot of boiling water and, voila!, you've got a highly detailed copper part. Or at least that's the way it's supposed to work. A plating set-up is easy to throw together with some plastic tubs and a car battery charger. It's a common jewelery-making technique. The chemicals can be bought  at any jewelers' supply house. Study the many YouTube videos to learn how it's done.

 

 

[Don Case]

Thanks guys. Yes I am considering casting. I'll have to do a little reading/watching.

[CPDDET]

I believe this process was covered somewhat in an issue of the Nautical Research Journal.