Can I hold 3mm thick brass plate for turning on a lathe ?

[Gas_mantle]

Hi all,

I'm hoping someone can help a beginner to this game.

I'm trying to make 2 brass discs 50mm in dia from a piece of 3mm thick plate, I could of course hacksaw and file to shape but as they are to be clearly visible pieces of a small brass engine I've made I'd like them to be perfectly round and both exactly the same.

Is there any easy way to turn the rims on my small bench lathe ? (neither plate will have a central hole)

Many thanks
Peter.

[Bertie_Bassett]

you could stick them with double sided tape to a face plate and use a center to hold them in place, use something sacrificial between the brass and the face plate so you can get the entire edge and a small block to spread the load form your center.

[10KPete]

It's not too hard to do but does take some set-up. I do it by sandwiching the thin stuff between two pieces of MDF (or
similar) and pressure chucking the stack. Cutting the wood and the copper to over sized rough really helps. If you're
not familiar with pressure chucking, it works like this; make the metal/wood sandwich, with one wood disc having a
little indent in the center of it, and squeeze it between the mostly closed chuck jaws and a live center. The little dent
in the one disk is for the center. Adjust the chuck jaws first so that your cut will easily clear them but keep the jaws
sorta close to the center to better oppose the pressure from the live center. Squeeze it up nice and firm. Take your
cuts. Worst case is the sandwich will slip on the chuck jaws so if that happens tighten the squeeze and take lighter
cuts. Done!!!

Pete

[mklotz]

Use some double-sided carpet tape to "glue" the two pieces together temporarily to prevent slippage when they're in the pressure "sandwich".  Take very light cuts.

[derekwarner]

Peter.......an alternate to the gluing below, soft solder the brass discs/plate squares to a brass former

You could also have a pre drilled bore in the former that would allow you bore the rims true and concentric on both the ID & OD
After the machining, simply heat & slide the completed discs off the former

[you mention a rim, but then note that neither will have a hole?]

A light sanding/lapping on the observe side will remove the evidence of the soft solder

PS....an ideal method of soldering the above would be to tin both brass surfaces then simply add additional ferric chloride liquid flux + a gentle lick of heat & the soldering task is completed

Derek

[Gas_mantle]

Hi all,

Many thanks for the help, it sounds like trapping the plate between the faceplate and centre with the help of double sided tape will do the trick. I intend to cut and file nearly to size first so the lathe work will only involve very light cuts to give me a neat circular rim.

Derek, at the moment as a beginner I don't yet have equipment to silver solder although it's something I'm considering.

Thanks
Peter.

[Jim Nic]

Peter.  From your last comment I think you may have got the wrong idea about what Derek was advising.  He advised the use of SOFT solder, that is the stuff used by plumbers or in electronic assembly.  Soft solder works at relatively low temperatures and is easily remelted to break the bond it has formed, it is also easily removed with abrasive paper.  SILVER solder, on the other hand, works at high temperatures and requires a lot of heat to melt and remelt, it is also comparitively difficult to remove.
I use soft solder to sweat pieces such as bearing halves together for machining quite often but I think that in your current case you are following the path I would take if faced with a similar problem.
Jim

[GWRdriver]

Easy . . . SUPERGLUE.  Face off a stub arbor and Superglue the discs to that.  When done heat the disk a bit and it will drop right off.  Ditto repeato.  I've done it many times, and light cuts are best.

[10KPete]

Please try it with out any glue, just once! I really works well, believe me. The method was taught to me about 40 years
ago and I've done all sorts of materials that way. The largest I can easily recall was something like a foot in diameter.

Pete

[Gas_mantle]

Hi all,

Thanks for all the suggestions, I hadn't even considered superglue !

As for the soldering issue, I'm sorry if I misunderstood but like I say I'm a complete beginner to this and know very little about soldering and possibly got confused with what was being suggested.

Peter.

[sshire]

Peter
All good suggestions that work. One of the best things about MEM is the amazing amount of knowledge that people are willing to share. So much of what I've learned has come from MEM.
Just in case you need yet another method...
http://www.modelenginemaker.com/index.php/topic,4711.msg88782.html#msg88782

[Gas_mantle]

Hi all.

I managed to successfully do what I wanted by holding a 40mm dia mandrel in the chuck then securing my work with double sided tape and finally holding it with the tailstock centre.

The job turned out to be a lot easier than I had expected, I had worries that the work may slip but everything held great. 2 minutes and job done 

Many thanks
Peter.