Double sided tape to secure parts for machining?

[GlennW]

What type of two sided tape sticks well enough to enable machining, but releases without rolling up the part?


I had one of those little one hour jobs over the weekend that took half a day.

3" x 8" x .140" thick aluminum part with a window in it. The .140" also stepped down to .100".

They supplied .160" material, so it needed facing as well as the step, so I figured the easiest way would be to stick it down to a bed plate for unobstructed tool access.

I face milled a bed plate, (CNC Mill) cleaned everything up and stuck the part blank down using half a dozen drops of Super Glue. Got it face milled and stepped, and shortly after I started to profile it, (1/4" end mill) it popped off the plate! Time to go home...

Next morning... I looked at my 3M two sided tape, the kind that is about 1/2" wide and 1/16" thick, and is somewhat spongy. Never used it for such a job, but it REALLY sticks, and I figured I'd ruin the part trying to get it unstuck! I was also concerned with the slight sponginess allowing the part to move.

Went to a different brand of Super Glue and got the part cut with no problem. Had to heat the tar out of it and pop it off using a scraper under the corner of the part though!

Thanks!

[Harold_V]

3M makes a double sticky tape that looks like masking tape. It was used with success for machining a bridge type casting, three feet in length, and roughly eight inches tall. Tape was used because other mechanical restraint systems were troublesome. The pads that had to be faced were required to be parallel within five thou. The casting was a permanent mold magnesium item, a part of the brake system of the Sergeant missile. (Yes, it had brakes).

It might pay for you to know that the casting was rough machined by other means, with tape used for the final passes only---with very light cuts taken by fly cutter.

Harold

[GlennW]

That sounds like the stuff!

I was in a shop quite some time ago and they had an entire table (bed plate) full of sheet metal parts that were stuck down, and the tape appeared to have little thickness IIRC.

First time I'd ever seen double stick tape used in that manner.

I'll investigate further!

Thanks!

[Harold_V]

First time I'd ever seen double stick tape used in that manner.

It's surprisingly effective assuming you clean both surfaces well (using a solvent---acetone, alcohol or MEK, or even a base solution like 409), and you don't use cutting fluid. If the surfaces have even a trace of oil, it doesn't work well at all.

Harold

[Mark Hockett]

Glenn,
I too have had some bad luck with two sided tape. I started using vacuum chucks and that helped. They are very easy to make with a CNC mill, ball end mill and some round foam gasket material.

[PixMan]

A little late, but two things came to mind for me:

1) Years ago when I worked in ceramics, we used a hot plate and a high-temp wax to secure the "doesn't stick to anything" ceramics to steel plates for grindng the thickness. I wish I could recall what it was by brand name, but it REALLY worked great. It was medium brown color and needed quite a bit of heat to melt. The best thing about it was that it was really reliable for leaving a thin, but perfectly flat film between the workpiece and the fixturing plate. We could hold a .001" parallelism tolerance, no problem.

2) Most recently (8 months of last year) I was working part time nights at a small job shop. They had started using a vacuum chuck system that they got from some well-known supplier of workholding systems, and the name completely escapes me as I write this. It's cool because it holds well enough to mill, but uses compressed air to fire a big cylinder that acts in reverse for the negative air pressure needed.

[whateg0]

This vacuum chuck thing sounds promising. I've had a few things that I have made recently that I clamped one half of down and then the other. The stuff I make doesn't need to be "that perfect", but this would sure be nice.

Guess it's time to fire up Google...

Dave

[DMF_TomB]

i use 3M 4032, double sided 1/32" foam tape. thin enough to not move much but foam allows sticking slightly irregular surfaces.
.
for example i stick 1/4" aluminum to a wood 2x4 which is held in a mill vise. i can cnc cut simple shapes with 1/4" carbide endmill. it is nice if cutting out a circle the center circle slug does not move around when the circle is completely cut. Tape sticks good, has enough give to it not not break holding bond easily. if anything this stuff sticks so well you might have problems peeling delicate stuff off without soaking in a solvent. also 3M tape 4032 is not cheap
.
there are sticky wax, wax sticks, wax tapes that are like used like melted shellac flakes to stick stuff together and when done items are heated or soaked in alcohol or other solvent to dissolve the glue.
.
i once used regular hot melt glue to stick aluminum to steel. on bringing the slightly warm piece to the sink to cool under cold water. the parts fell apart. i believe the expansion difference in aluminum and steel and the fact that the "glue" had no give to it. the bond broke extremely fast.
.
http://www.willbell.com/ATMSupplies/ATM_Supplies.htm
telescope making supplies check section on Rosin, Pitch, Beeswax, and Blocking Pitch
......used for holding glass while grinding, comes in different hardness.
.

[BClem]

Try JB weld. Works fine for all but very heavy parts. Scrub an aluminum or steel plate and the part or material super clean (water break clean) with comet or ajax and bond them with JB weld. Clamp the plate..... You can also orient an odd shaped part to be machined. Turn the plate over after machining and whack it with a hammer - the part fractures loose, then clean the JB weld off.....

There is a product specifically formulated for this and used in aerospace modeling - so; it's hard to purchase and very expensive. JB weld works just fine.

BClem

[GlennW]

Super Glue has been working fine for me on small thin parts like these .025" thick alum shims.

I just put some 4" x .5" thick 6061 scrap in the vise, skim it with a face mill, scuff it a bit with Scotchbrite, and glue the sheet to it.

A razor blade (I can post a pic of one, Harold) under the corner pops it right off without distorting the part at all.

[Harold_V]

A razor blade (I can post a pic of one, Harold)

I am lead to believe that owning a razor and/or blade is a criminal act. I avoid them at all costs.

Harold

[kapullen]

I frequently use a vacuum fixture for plate and sheet jobs.

Here is a job from a week or so ago 12" by 24" by 3/16" thick
running on the Fadal. This was a two part deal.

The customer supplied the vacuum plate material.

http://www.youtube.com/watch?v=Tdfldha4wx0

I don't do all that criss cross milling on the fixture but just a couple channels
to the edges from the vacuum output hole.

If there are holes in the center, I'll just spot drill them not to break the vacuum.

The vacuum pump is a 12 volt gast pump from Grainger that also operates the train brakes on the Hustler
locomotive.

I have a regular plastic job coming up again of 144 pieces about 1/4" x 2" x 4".
I run that one in threes, saw them apart when done. That increased the vacuum area.

Kap