Cutting brass disks from sheet

[raynerd]

I`ve been wanting to post this question for a while.
Basically, I want to cut disks from brass sheet, various diameters from very small to upto 3", possibly even 4" diameter. Don`t get me wrong, I can easily do this and I`ve done it many times. Hack off a square of sheet brass,, trim the corners, centre drill, mount on an arbour and turn to size. However, I can purchase brass disks at a price - much much higher than buying the sheet of course. These disks come perfectly round, to any size specified and more interestingly, no centre hole! The seller also is cutting these from sheet and will not want to waste money so I`m pretty sure they will not be cut from square. One method would be to cut a square of brass, glue or tape to a sacrificial wooden back plate and turn to size - risky but I know it can be done. However, I know this ISN`T the method being used since the brass still has its protective backing on both sides and you can see from the tare edges that it has been on during cutting.

So my question really is what methods would you guys suggest to allow me to cut brass disks from sheet with low material wastage? I can have a centre hole if necessary but I`m keen on thoughts as well for how else the seller can be cutting the disks mentioned above without the centre.

One inportant point is that we are talking about CZ120 leaded engravers/compo/hard brass - so can be machined very well, unlike cheaper normal "sticky brass" CZ108.

 

Chris

[rleete]

Disks you purchase are most likely punched from sheet or strip. 

[John Stevenson]

CNC turret punch, do any shape you want.

[BiggerHammer]

However since you also asked "how we would do it" here goes. Hope I able to explain this. On the drive side of the lathe go with a backing board as you said. However it should not be sacrificial. It needs to be smaller than the size of disc you wish to cut. Place the disc on the "drive surface" and use a bull nosed live center in the tailstock to hold it in place.

Now after that failed  I would try to "spring load" the live center so it would push with a constant pressure insuring the disc did not move.

[mattinker]

I glue the sheet metal to the rotary table with double sided tape via a piece of sacrificial mdf and cut it out with a small milling tool. You could do this on the lathe, but I've found it had a tendency to stretch the edges.

You high speed spindle would be very nice for this with a 3mm cutter in it!

regards, Matthew

[raynerd]

Interesting about the stamping. I'd not seen one of those turret punches before!  as I'm sure he advertised as "not stamped" so that the edges are not rounded! Looking at the edges of some of the purchased disks I've got, there does look to be almost teeth marks, certainly isn't a smooth finish on end cut.

[raynerd]

Sorry for the errors in the last post...it posted it without me finishing and now can't edit it! Bloody tapatalk app - who asked Eric to install that piece of ... ;-). ( joke - me! )

So with the methods suggested, you are basically still going to lob off a square of metal. I think I'm in tight arse mode again and was hoping to get a method to allow you to utilise the full sheet more! I.e cut a row of circles and then take the next row out with the tops of the circles in the interlaced between, if that makes sense. Think I'm in dream world there.....and besides with all the disks different sizes, probably wouldn't work out anyway!

Interesting thoughts so far.

Just curious, I've never used a bandsaw. Would that allow you to get a bit nearer a circle shape from the sheet? Having never used one, not too sure how tight you could turn through sheet metal?

[awemawson]

a/ Band saw would need a VERY small blade depth to cut clock wheel sized blanks.

b/ There are things called Circle Cutters that pinch a sheet between two pads, rotate the sheet on a vertical axis and nibble the edges. Never seen them small enough for clock wheels

I would use one of two methods: either a/ super glue the sheet to a sacrificial piece of plywood and trepan  the disk on a vertical mill, or b/ roughly cut a disk by whatever means and pinch the result between a faced off bar in the lathe chuck and a suitably made pad (*) on a rotating centre in the tailstock, then turn to finish.

* Pad can be a short length of bar faced both ends and one end deeply centred to sit on the rotating tailstock centre.

[John Stevenson]

 I.e cut a row of circles and then take the next row out with the tops of the circles in the interlaced between, if that makes sense. Think I'm in dream world there.....and besides with all the disks different sizes, probably wouldn't work out anyway!

No that will never work   

[Meldonmech]

             When making clock wheels, roughly mark out in pencil where the wheel crossings are, drill two diametrically opposite holes in the spaces as near to the inner rim as possible. Attache to a wooden mandrel 10mm larger than the wheel dia. using two wood screws. Grind a trepaning tool about 1.5 wide and trepan the disc using a slow in feed. The tool should not be square ended in plan view, but should be tapered like a L.H.knife tool, in orde rto produce a clean edge on the wheel blank. Using this method I start with a square blank.

[RussellT]

Hi Chris

How about just cutting them out with a nibbler.  The type that attach to a power drill will cut 2mm brass and can do tight corners with a cut width of about 3mm.  In my experience it's difficult to follow a line exactly so I'm not sure how much wastage there'd be.  Maybe you could make a fixture to rotate the sheet brass accurately.



Russell

[smiffy]

Hi I clamp the sheet brass to the drilling machine table ,with a suitable piece of wood between the table and the brass then i use a starret hole saw with the pilot drill removed and useing a very slow speed cut a disc out of the brass sheet .It does need a very ridge set up but i have cut dozens of discs useing this method  Hope that all makes scence. Mike

[Fergus OMore]

Metal Box Company would have used a 'Bob and Aunty' male and female punch.

And they did it for billions of billions of roundy things in plate metal.

[jiihoo]

Haven't done this so this is purely theoretical, but how about punching (or hole-sawing without a center drill) 2 mm or a little more oversize and then turning to size?

If this works, it would give you a not-punched edge and minimize the material wastage. The turning you could do with the blank sandwiched between two plywood rounds between the headstock and live center on the tailstock and thus no center hole.


Jari

[raynerd]

Hi Guys
Many thanks for your interesting suggestions! It does seem likely that the seller could possibly clamp the sheet between two "pads" and turn it round in the lathe.

Regarding the actual method of me turning up brass disks, I`m interesting in this idea of trepanning as suggested by awemawson and Meldonmech

Meldonmech - you said something very interesting. About 10 years ago I visited a clockmaker, bearing in mind I hadn`t even seen a lathe until that day and your method of cutting the the wheel was exactly the same as that which he used! Your message brought it all back. Drilling two small holes where the crossing out will be, mounting on a wooden backplate and using a tool to cut (trepan) the wheel. I do appreciate you have tried to detail the profile of the tool...could you give me a little more info on what the tool should look like as I must admit, I can`t picture it!

[andyf]

Chris, I used a home-ground trepanning tool to cut the biggish hole in the 6mm rectangular steel plate in the pic below, before boring it to finished size.



The tool was rather like a parting tool ground on the end of a square HSS blank but, viewed end on, the sides of the blade were curved to match the sides of the groove it would make, and then a bit more to give some relief.

If your brass sheet is relatively thin, you might get away with a threading tool plunged straight in,
particularly if you can work halfway in from one side and flip it over to finish the job. Then the circumference could be turned to size.

Andy.

ed them b

[BiggerHammer]

Do you think he might be using a water jet cutting table? No fuss no muss. Clean cuts, no rounding of the edges, and can cut to any size. Just a bit expensive I would think.

[Deko]

Jari, I have cut many round blanks out as you say,with a hole saw and no center drill. Just clamp the plate to a piece of wood on the drill press, job done !!!

Cheers Dek.

[awemawson]

Here you go Chris:

http://www.ebay.co.uk/itm/SAHINLER-IDK-1-CIRCULAR-CUTTING-MACHINE-/271134709288?pt=LH_DefaultDomain_3&hash=item3f20e35628


Regards,

Andrew

[NickG]

Could u just make a custom fly cutter type trepan ing tool?

[DMIOM]

Here you go Chris:

http://www.ebay.co.uk/itm/SAHINLER-IDK-1-CIRCULAR-CUTTING-MACHINE-/271134709288?pt=LH_DefaultDomain_3&hash=item3f20e35628


Regards,

Andrew

and if you want more info on these Chris, Ralph had one - although those look possibly bigger than you might want in your basement clock works!

 ..... maybe there's scope for one of our casting crew to make a tiddly version suitable for clock wheels? 

Dave

[Meldonmech]

Chris
           As Andy pointed out the grinding geometry should be similar to a parting tool, ground initially to to the same diameters as each side of the slot you are cutting, then given side clearances to prevent binding. The aim is to produce a disc with a square edge to avoid any further machining, so instead of having a perfectly square end on the tool, grind a small amount off the left hand side to produce an angle. This will ensure you will break through on the outer circumference of the disc, leaving any burrs on the scrap side. The tool must have zero top rake to ensure the tool is not grabbed by the brass. I would advise a little practice on scrap before moving onto an important clock part.
                                                                                                              Good Luck David

[sparky961]

I'm not 100% sure it would work to cut brass since I've never tried yet, but can you not find a shop that does laser cutting in your area and see if they would do it?

Maybe this is easier said than done for most people, but we have a few of them where I work.

-Sparky

[raynerd]

Hi sparky, not willing to pay for laser cutting as they aren't critical in size and different sizes, so wasted money.

Just to let you guys know since this is still attracting comments and I just wanted to say I am trying your ideas.

I've fitted a circular saw to my pillar drill and sure enough it'll cut with no centre drill if I take it slow at the start. I appreciate in my original email I ask about a disk with no centre hole but I've modded the centre drill to make a much smaller drill and actually it is quicker still to simply use my bosh drill to cut the disks using the circular disk cutter with a moded tiny centre drill.

The idea of trepanning is still most definitely something I want to try soon.

Thanks for all the interesting ideas and replies.

Chris

[raynerd]

Rather than start a new thread, I just wanted to ask a similar question:

We have a big 6 foot standing bandsaw here at work and just to test it, it took the corner of a 3mm plate cz120 leaded brass sheet without any issue...in fact, cut through it like cheese. Would a cheapo bench top bandsaw do the same? I certainly know a friend on here uses a bandsaw to cut through brass but I expect his is a bigger machine than the cheap bench top ones I`m looking at. Any thoughts?

Phil - what bandsaw do you use?

[Fergus OMore]

What do you regard  a cheapo bench bandsaw, please? 
I just adjusted one of these cheap 6 x 4 bandsaws. Bit of a so and so to adjust but once going and adding a few mods, will cut through 37mm cast iron marking out table.  As for the bench stuff, I've heard of the 'better than sliced bread' and 'wouldn't cut sliced bread'

I had an old Burgess, worked it to death, but I doubt if you will find one that is not ready for the scrap head. If you find a good one, you'll enjoy every clank, rattle and bang-- but it will cut metal.

[mattinker]

I have a Clarke 4x6 metal  bandsaw that will cut up railway track! It can be used in the vertical position the standard blade width is 13mm and kerf is too narrow to cut around corners. I use a 10 14tpi variable pitch blade for everything except fine tubing, for which I have 24tpi blade. These saws need tweaking out of the box, it is important to change the oil and clean the worm drive before doing anything else.

There is a yahoo group on which you can find a lot about modding and trouble shooting these saws.

http://groups.yahoo.com/group/4x6bandsaw/

Among the things I have done to my saw is I've added coolant using a fountain pump and a hydraulic down feed to make the the cut more controllable.

Regards, Matthew

[awemawson]

Bandsaws tend to fall into two categories, for wood, or for metal. Basic difference is the speed of the blade however blade guides will be more substantial on the metal ones. I use a Startrite one that crosses both areas in that it has a 10:1 gearbox that can be introduced to reduce the speed to that needed for metal cutting. Of course the blades are different for wood than for metal but what ever material you are cutting, the blade pitch will need to be such that at least two, and preferably three, teeth are cutting at one time, so your 3 mm blank would need a fine toothed blade of 1 or 1.5 mm pitch. To cut a good straight line you need not only good guides, but also a deep blade. To cut tight curves you need a shallow blade. So your guides need to be either adjustable or interchangable so that the tooth profile runs outside the guide otherwise the 'set' of the tooth will be squashed by the guide. Guides can be either a slot cut in a very hard material, or an arrangement of ball races where the 'outer' guides the blade. For some reason that I don't understand, the 'slot' variety are considered more accurate (I would have thought it to be the other way round!)

[Alan Haisley]

Chris,

Try a boring head in the mill. Cutter can be unhardened drill rod for a test since that will cut brass just fine - at least once or twice. You will need to experiment with the tip geometry some to get it right but you should be able to cut a variety of either centered or centerless blanks from a sheet with minimum waste. Depending on your boring head, you should be able to get just about any size circle desired. With the cutter shaped right they could be both very accurate and have a finished rim. If you preplan the crossings you should be able to screw the material down to either smooth wood or mdf so that nothing breaks loose just as the cuts finish. (Lots of tiny wood screws.)

Alan

[fcheslop]

Maybe I'm looking at this wrongly.Why not just use a jewelers saw to cut them out then friction turn them between two backing sheets.Very little waste and no centre hole.