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Holding sheet metal on milling table

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RMA28/01/2019 11:28:18
120 forum posts

Good morning all

I'm sure someone on here has the answer. I want to create a chequer plate effect to some thin brass, roughly 1.5 inches square, and as the pattern will go over the whole area, there is nowhere to clamp. I intend to use the mill as a shaper using a vee tool.

Cuts will only be a few thou, so I thought of using double sided tape directly to the table, but there are so many variants and if it's too thick it might move or depress with the cut. Has anyone done this and what type of tape can you recommend?

Any other ideas will be welcome. Thank you

Clive Brown 128/01/2019 11:34:22
229 forum posts
6 photos

Soft solder, or perhaps superglue, onto a larger, thicker piece of brass?

peak428/01/2019 11:34:31
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739 forum posts
65 photos

Will you be able to see the back on the finished model?

If not, how about some soft solder paste or similar to something thicker, or even a superglue, carefully selected, which will break down with a bit of heat.
If you want to avoid heating, a perforated block of metal with the brass superglued to it, would probably release its captive brass plate if you inverted it and filled the holes with acetone.

Bill

Looks like we were typing at the same time Clive, but you're quicker than me.

 

Edited By peak4 on 28/01/2019 11:35:47

Martin Kyte28/01/2019 11:37:17
1419 forum posts
9 photos

Double sided sound fav to me.

Martin

John Paton 128/01/2019 11:42:30
152 forum posts
6 photos

Unsure what's aleyouarestriving for but at smaller scales the easiest way by far to do this will be by etching the pattern onto brass.

At its simplest chemically degrease the surface and apply Letraset diamond hatching then etch with ferric chloride (as sold for making printed circuit boards)

For more specific patterns do artwork and photo print onto plate before etching

SillyOldDuffer28/01/2019 12:23:45
4271 forum posts
880 photos

I'm a fan of super-glue for holding thin work in place. The glue spreads thinly so the job stays flat on the mount, and it's much faster and far less fuss than soldering. Once finished the bond is broken by boiling water, and any glue remnants are fairly easy to remove with nail varnish remover (acetone). In comparison solder requires tools and is much harder to apply and far harder to remove.

Main thing with glue is to to get everything really clean first - even a tiny trace of grease weakens the joint massively - and not to overheat the bond while cutting.

Dave

Michael Gilligan28/01/2019 12:36:00
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13057 forum posts
570 photos

Thin [*] double-sided tape should hold the material, but it may be difficult to remove the workpiece without bending it crying 2

I would favour the traditional Shellac, and a sub-plate.

Edit: or, as Dave suggests, a suitable 'superglue'

MichaelG.

.

[*]

SupaDec does a version; intended, I think, for vinyl floor-coverings.

3M is probably the best manufacturer of such stuff.

 

Edited By Michael Gilligan on 28/01/2019 12:38:29

Edited By Michael Gilligan on 28/01/2019 12:53:51

Tony Pratt 128/01/2019 12:44:48
854 forum posts
2 photos

Double sided tape for sure, hair dryer or similar heat will soften the glue.

Tony

JasonB28/01/2019 13:02:17
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15330 forum posts
1580 photos

Cut the pattern while still part of a larger sheet then cut out the bit you want, that way you have the rest of the sheet to clamp as you wish.

I thought Michael may point out that the diamonds should be lower while the "lines" should be raised rather than cutting the lines.devil

Edited By JasonB on 28/01/2019 13:03:41

RMA28/01/2019 13:21:31
120 forum posts

Thanks for all the replies/suggestions guys.

The parts are already cut out by laser as part of a kit hence the need to hold from beneath. Ideally I want to 'stick' them to the bed, so I'll try tape first. They shouldn'y distort when moving as they are 1.2mm thick, so heat and a razor blade will be tried.

Will update when finished, it might help someone else. Thanks again

Michael Gilligan28/01/2019 13:49:29
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13057 forum posts
570 photos
Posted by JasonB on 28/01/2019 13:02:17:

... I thought Michael may point out that the diamonds should be lower while the "lines" should be raised rather than cutting the lines.devil

.

yes ... But Michael showed restraint, and simply answered the question.

MichaelG. angel

IanT28/01/2019 14:02:23
1256 forum posts
128 photos

"Cuts will only be a few thou..." - so very delicate work RMA and I think you already understand that you will need to work on a flat and unyielding surface.

As Michael suggests - use a sub-plate but make sure it is absolutely true/flat to the worktable before you super-glue the work to it (using a weight). Removable pins in the sub-plate will help you to edge align the work piece correctly to the sub-plate (which can be clocked true beforehand). I've not used a mill to do this kind of fine cutting, as I have a hand shaper which I think is preferable for this kind of small application - but don't see why it wouldn't work.

For true chequer plate - you really need to etch the work as JP suggests.

Regards,

IanT

Adam Mara28/01/2019 15:03:19
67 forum posts
4 photos

A trick we used at work for holding small pieces for routing was to cut a hole the size of the plate in a larger piece of scrap material slightly thinner than the workpiece. Both fixed to the sub plate with 3M VHB tape, then clamped to the machine bed. Fairly thin soft aluminium was used as a sub plate, as it was easier to 'peel' off.

Joseph Noci 128/01/2019 15:41:30
476 forum posts
817 photos

If its only a few thou deep, and you are happy with depressing the chequer section, then what about grinding a diamond form to a piece of silver steel rod and pressing the depression into the brass? Sort of as you would stamp letters/numbers onto a dial / indicator face.

I know the brass is hard, but a few though on a diamond form say 4mm x 3mm might work.

Else, place the plate diagonally and clamp one half, engrave the lines on the unclamped half, and clamp the now done half, then remove the previous clamps, etc, etc..

Joe

Chris Trice28/01/2019 16:06:29
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1360 forum posts
9 photos

Can you cut a larger sheet, clamp it, produce the diamond pattern, then cut it to size? You don't say how thick your thin piece is.

Andrew Johnston28/01/2019 16:38:52
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4633 forum posts
522 photos
Posted by Chris Trice on 28/01/2019 16:06:29:

You don't say how thick your thin piece is.

Read a few posts back. smile

Andrew

Tim Stevens28/01/2019 18:03:18
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1019 forum posts

Can I suggest that a thin sheet of brass is very likely to flex - possibly becoming tight in the centre or vice versa - unless it is firmly attached all over to a thicker sheet. To do this you need to sandwich the pair under pressure between two flat surfaces, while the adhesive sets. As for the glue itself, tradition would say shellac, such as knotting, applied evenly to the thicker element, allowed to dry horizontally, add the thin brass, and warm carefully and evenly with eg a hair dryer, and put under pressure (four volumes of an encyclopedia, perhaps) while it cools. Leave one edge of the thin sheet overlapping slightly (2mm) so you can hold it when warming the pair again to separate. Then remove traces of shellac with alcohol (meths, burning alcohol).

Or do the same sort of things with Loctite or a similar product - but you need a fancy solvent to get traces off afterwards.

Hope this helps - Tim

Neil Wyatt28/01/2019 22:48:16
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15947 forum posts
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Posted by Tim Stevens on 28/01/2019 18:03:18:

(four volumes of an encyclopedia, perhaps)

See, they DO still have a use

Neil

David George 128/01/2019 23:12:19
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783 forum posts
282 photos

I used to machine thin aluminium plates using a vacume pump. We had a plate with an o-ring in groove just inside the edge of the piece there was a hole inside the o-ring connected to a cross hole which was connected to a vacume pump switch on the pump and you cannot move the piece. The pump was hired for about £40.00 a day but you can machine a lot of pieces in a day.

David

Chris Trice29/01/2019 10:26:46
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1360 forum posts
9 photos

Having thought about this, I'd epoxy the sheet to a piece of good quality plywood (after scouring the back of the brass with a bit of abrasive paper) and clamp the plywood to the table. Once machined, heat the brass with a hot air gun until the bond with the epoxy is broken.

Edited By Chris Trice on 29/01/2019 10:27:15

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