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Gang drilling stainless steel sheet

ShaunM

Aluminum
Joined
Apr 13, 2015
We’ve got a job where we need to put qty (144) ¾” holes in 20 gauge stainless sheet steel parts (unsure of alloy, but it’s a stamped/formed part if that helps). These are purchased parts that we are modifying for our needs. Quantity of 2000-2500 parts. Tolerances are loose enough where a twist drill would be good enough if that’s what we end up using.

So far our plan is to stack as many of these parts together as we think we can, sandwich them between two aluminum plates (fixture), and start punching holes. We are concerned a twist drill might be too grabby. An annular cutter/rotobroach was considered but it seems the slugs would build up and plug up the tool. Spiral ramp an endmill? Maybe we're over-thinking the whole thing.

We had a local shop water-jet a few. The results were acceptable but the price was outrageous (didn’t seem like they actually wanted the job). A different local shop lasered a few and the price was much more reasonable, but the results were awful. Out-of-round, burs, etc.

Any suggestions? We have a late model VF4SS and VF6SS in the shop. We even tossed around the idea of approaching a stamping company to see what a tool would cost to form the part and punch the holes.
 

sfriedberg

Diamond
Joined
Oct 14, 2010
Location
Oregon, USA
3/4" twist drills in sheet metal don't strike me as fun. The gang drilling between plates would improve things, true.

Can you get the parts to lay flat on a platen, with a reasonably generous clearance between any hole and any formed part that rises off the platen? If so, a sheet metal shop with a CNC large-bed punch can probably whip out those holes pretty quickly. As in bam-bam-bam-bam..., next part. Normally those punches are used with a flat sheet, so a shop might be leerly of working on formed parts. But it's worth inquiring.
 

Bondo

Hot Rolled
Joined
May 14, 2011
Location
Bridgeton NJ
A unipunch or similar custom setup would be the way to go.

Drilling 20 ga SS, even stacked, is not going to go great. A hougen annular or hougen sheet metal annular works, but will leave burrs.
 

ShaunM

Aluminum
Joined
Apr 13, 2015
I agree 100% a VMC is not the way to process these parts. But, for reasons I cannot explain, the boss insists on running these on "the cnc". I do appreciate the unipunch reference - they are a good solution to keep in the back pocket for future projects.

It sounds like we will just have to experiment and see what works and what doesn't (drill, mill, annular, etc.). I'll update once we run some. Thanks again for the responses thus far.
 

Scruffy887

Titanium
Joined
Dec 17, 2012
Location
Se Ma USA
Fiber laser will be stupid fast if the operator knows what they are doing. The HAZ and "slag" on the back of a 20g part should be able to be removed with your fingernail. If you can find or feel it. I cut loads of 16g 304SS. Kerf is .0393 and HAZ is about zero. You may have brought it to a hobby laser shop?
 

ShaunM

Aluminum
Joined
Apr 13, 2015
You may have brought it to a hobby laser shop?

Very possible. The water jet and laser trials were done before I got involved. I've just been asked to design a fixture for the VMC.

I'm also a little concerned with how well you'll compress the stack in the center area if this is a roughly square grid of holes. I'd expect the Al plates to bow, giving you much more burrs as you get towards the middle.

Whatever the actual grid geometry and spacing, think about center clamping and how you can mitigate bow.

Thanks for the tooling advise, we're not opposed to a two-tool operation if that's necessary. And I share your concern with compressing the center adequately. One option may be to put ribs or something on the top plate to give it some rigidity so we can get a way with clamping only the outside edges.

Get an annular cutter that is sharpened for stacked material, the grind is opposite the standard cutters so the little slugs do not need to be removed.

Sounds like a winner. Can you share any brands or links for something like that?

For reference, these parts are essentially baker's trays, 13"x18" with the holes in a 12x12 grid pattern. The spacing in the 13" direction is tight so there isn't a lot of room for fixturing. The 18" direction has more flexibility.
Thanks again, all.
 

ChipSplitter

Titanium
Joined
May 23, 2019
Location
Maybe
Very possible. The water jet and laser trials were done before I got involved. I've just been asked to design a fixture for the VMC.



Thanks for the tooling advise, we're not opposed to a two-tool operation if that's necessary. And I share your concern with compressing the center adequately. One option may be to put ribs or something on the top plate to give it some rigidity so we can get a way with clamping only the outside edges.



Sounds like a winner. Can you share any brands or links for something like that?

For reference, these parts are essentially baker's trays, 13"x18" with the holes in a 12x12 grid pattern. The spacing in the 13" direction is tight so there isn't a lot of room for fixturing. The 18" direction has more flexibility.
Thanks again, all.


A decent laser would burn through all of those parts before you could set up a VMC to reliably run even one. Put a part on MFG.com and see what happens.
 

Rob F.

Diamond
Joined
Aug 5, 2012
Location
California, Central Coast
Sounds like a winner. Can you share any brands or links for something like that?

For reference, these parts are essentially baker's trays, 13"x18" with the holes in a 12x12 grid pattern. The spacing in the 13" direction is tight so there isn't a lot of room for fixturing. The 18" direction has more flexibility.
Thanks again, all.

Both Hougen and Jancy (fein) make stack cut cutters, probably others as well. I primarily use Hougen and they are listed in their catalog. Be sure to look or ask for "stack cut". Another term used for these is I.D. sharpened, (similar to a standard twist drill. The "normal" way annular cutters are done is O.D. sharpened, these will just spin on the slug if material is stacked.
 

BT Fabrication

Stainless
Joined
Nov 3, 2019
will it fit in an ironworker with a 3/4" punch? that would take one at a time to prevent deforming parts but would punch as fast as you can load them. check out Cleveland tool, they make custom die sets for everything. they make all the punches for edwards and other ironworkers.
 

rcoope

Stainless
Joined
Sep 25, 2010
Location
Vancouver Canada
+1 for laser. It's unfortunate that the OP got bad results from testing. I get 20Ga laser cut routinely and the cuts are excellent with no finishing required.
 

Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
I've actually had great success drilling stacked sheets in a VMC.

I make a bunch of disposable drill templates this way. I shear up all of our random thickness rems, stack them up about 2" thick and peck drill them all at once with a HSS twist drill. The holes are clean and burr free. Pretty amazing really. You don't need to worry about long stringy chips that's for sure.

When you stack thin plates the drill tip has something to pilot into so it drills a nice round hole. I don't even use a cover plate. The top sheet is thin just like the rest of them. This is 16-20 gauge usually EG so it doesn't rust. Not stainless, but I don't think it would be all that different.
 

gbent

Diamond
Joined
Mar 14, 2005
Location
Kansas
Another alternative is a brad point or sheet metal point drill grind. One at a time only, but will drill a clean hole easily. Much better than a standard twist drill grind.
 








 
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