Newbie- thin workholding

[tonyaimer]

Greetings All


I am awaiting delivery of my machine. This may take a month or two to get to South Africa but I am going to be monitoring this forum in oder to become familiar with the issues of owning and running this machine.

I have a well equiped home workshop but no CNC skills to speak of at this time.

I am autocad literate and am starting in on Inventor for solids modelling.

My first question deals with the holding of thin work pieces. One of my applications for the machine is to cut out model train parts in brass sheet in thicknesses to great for etching. I am into gauge 1 live steam.

How best does one hold thin sheet for cutting with a small diameter end mill or slot drill. Perhaps one needs a sacrificail backing piece?

Any advice or guidance would be welcome.

Tony Aimer


Johannesburg
South Africa

taimer"at"zanet.co.za

[apeman88]

Cutting thin material is very hard to do if you want a clean cut especially on soft material like Alu or Brass. Just a few months ago I cut a bunch of panels out of Alu (.08" and .1" thick) with instrument gauge, switch, monitor, LED and etc holes. It was such a pain to do if you want a clean cut. You need to slow down the IPM way down or the endmill will grab the material and bounce/vibrate your sheet up and down and the cut edge will look like you used a dull hacksaw.

I had to slow my cut down to no faster than 5ipm and sometimes even 2ipm if cut (hole) is too far from the hold down.

Also... use a piece of wood or plastic between the sheet metal and hold down clamp. If you clamp down directly without the spacer.. you will dent ALU or brass.

You can use a piece of plastic and lay over the sheet metal than you can go faster... but you would be wasting that material. I guess if you are running a production... it might be worth while to do so and use that as the jig or template for other cuts.

Ken

[acidcustom]

try this tape
I haven't used this yet as I will be picking it up soon from my friend in Dallas when I visit him but I have heard this is a good way to go
http://cgi.ebay.com/Hold-down-tape-f...d=p3911.c0.m14

[holbieone]

super glue

hit it with a torch real quick to release it

[Freddy Bastard]

If you plan to do a lot of thin material cuts, you could use a vacuum table. I've done one for myself and it work's fine. I've used double-side tape too and it work fine.

[300sniper]

has anyone used any of the mitee-grip heat activated products made by mitee-bite? i have had a few projects that were completely removed from the surrounding material and no longer held by clamps. this caused chatter toward the end of the cut. this sounds like a good product by reading their description but would like some feedback from users.

http://www.miteebite.com/

[neilw20]

Mix some shellac and methylated spirit.
Place on sacrificial surface under pressure with a weight and allow to dry.

When machining finished soak in methylated spirit or just knock it off because fairly brittle.

Heat from machining can release super glue when you least expect it.
Another strange effect of super glue is it goes liquid when ultrasonic vibration is present. I guess due to heating effect. If you have an ultrasonic welder, then a few seconds can release super glued items.

[xcayba]

I imagine that this would be similar to milling PCBs as they need to be held down evenly, not just around the edges. The super glue can be released with acetone (or a flash of heat, from previous poster) so I'm told. The movie referenced below shows both double sided tape and super glue hold down methods. I've been using double sided carpet tape from my local hardware store to hold items down.

For your specific situation, I would suggest that you superglue the metal to a piece of sacrifice material, such as 1/8th inch plastic, plexiglas or polycarbonate. This will make it thicker and less prone to chatter and you can cut all the way through it. When all done, sprinkle generous amounts of acetone over the surface and help it work down between the sacrifice material and metal to release the bond.

YouTube - Milling a fine trace double sided pcb

YouTube - Milling a fine trace double sided pcb

[tracebender]

xcayba, thanks for the nice video! What software are you using to mill the PCB?

We use an LPKF (lpkfusa.com) machine at work; we use their software called Camtastic to convert Gerber files to a file that is then run in their proprietary program called BoardMaster to drive the router. I've been thinking of trying to do this at home on a CNC mill but have no idea what type of software I could use to do this.

BTW, we do have the vacuum table option for the LPKF machine and it works great. The sell disposable permeable material that goes under the board your milling. For through cuts this material protects the vaccum table and can be used for many boards before replacing. It probably wouldn't be too hard to design similar table for a cnc for those that do a lot of PCB or thin panel work.

[xcayba]

I can't take credit for that excellent video. That is something I found when looking for information on how to cut PCBs myself. I hope to do this one day soon, but have never tried it. The software that is used is mentioned near the beginning of the video though.

[tracebender]

Thanks, I must have gotten distracted when they flashed up the info about PCB-Gcode. It looks like a user program for the Eagle Cad PCB files into G-code. I might have to give this a try if I can ever decide between buying an off the shelf CNC or converting my X2 to CNC

[rwexec]

Standard flute cutters tend to lift the material due to the helix of the cutter.
Try getting a left hand helix which will push the material down on the fixture plate.
Use carpet tape, sticky on both sides.