Cutting Leather

[nat_wheatley]

Is there bit that might do a clean pocket in leather? The application is cutting 3/32" deep pockets in 3/16" leather. We tried a down spiral @10K RPMs/2ips, and got very ragged edges. Bottom of the cut was fine, but the outside edges of the pocket were not good. Tried both climb and conventional directions, bad edges with both...

[Brady Watson]

You need more RPM....crank that puppy up to max RPM & then try it.

-B

[nat_wheatley]

Will do, thanks. All I know is plywood and melamine, and thought the 10k might be on the high side...

[nat_wheatley]

This is a very rough sketch of what they're considering buying a SB/Tyro to do. It's a shoe part, the hatched area is the area that gets pocketed. They outside shape is stamped by a die. Sounds like they do lots and lots of these.

At the moment, the process is to clamp the blank cutout in a jig, manually score the outside cuts of the pocket with a small handheld razor, guided by the edge of the jig, then use a hand held router, also guided by the jig, to hog out the material.

The thought is that they may have to continue to manually score the edges of the pocket, but could then send to the bot to clean out the center.

Will try higher RPM's, but open to any and all suggestions. Thanks

[ironsides]

Try freezing with CO2 gas or Dry Ice just prior to cuting.

George

[Brady Watson]

Good idea with the freezing...

Generally speaking, the softer the material, the higher the RPM AND number of flutes you need to get clean cuts. The converse holds true for hard materials. When you mill steel, the RPM is much lower than anything we do on our routers. When we route non-ferrous metals, we use a single O flute tool and keep RPM 13k-15k and rarely go faster than 1.5 IPS.

When trying to dial in on a challenging or new material, you want to take a step back and really ask yourself what is going on where the bit is cutting the material. The soft & stringy nature of leather makes the tool's flutes want to grab the material and rip out chunks, because it lacks the rigidity to stand up on it's own when the tool goes to cut it. Remember - every force has an equal and opposite force pushing back on it....So if the material is flimsy or soft, it's going to act like a big rubber band.

When you increase the number of cutting flutes OR RPM, you effectively lighten up the chipload, or size of the bite the tool is taking out of the material. The smaller the bite, the less likely that the material behind the part's edge will get sucked in by the cutter. If you take lots of small bites, you'll get a better cut than if you take larger bites. You will also have a much easier time holding the material down because, as stated earlier, every force has an equal opposite force - this opposite force equals your hold-down efforts, whether that is DS tape, vacuum or clamps.

Does this make sense?

Lots of people cut (mainly 3D) pink/blue foam at 9-10k RPM. The router or spindle is totally happy doing this & can work all day long this way. The problem is, the finish on the part is really horrible - many times chunks are missing or there is the telltale texture of corn rows, foam 'hairs' and strings. Most people chalk up the low quality to the material itself. If you use a 4-flute tool (for 2D or 3D) and crank the RPM up to 18k or more, the results are quite different...

-B

[nat_wheatley]

George,

Great idea. I've put a blank in the freezer, will see how it cuts tomorrow.

Brady,

That does make sense. Thanks very much for taking the time to post that.

Nat

[shoeshine]

I have done 1 (and exactly 1) leather job on the bot. So I am hardly experienced, but here goes.

This was for a leather inlay for a desk top. I spraymounted the leather to a piece of mdf board. I used the vinyl drag knife from widgetworks to score the leather using an "on" profile. I then used a 1/8" 2 flute endmill with an outside profile to do the cutout. (19k @ 2 ips if I remember right)

a little cleanup with an xacto afterwards, but all in all, worked pretty well.

Chris

[nat_wheatley]

Standard freezing, didn't seem to have much of an impact. Ran bit(s) at 18K RPMs. I would guess that the colder temps of the CO2 gas or dry ice may have a different effect.

The drag knife idea sounds like it could work here. It's just the top skin that needs a clean cut around the pocket. The rest of the cut doesn't matter as the void is them filled with hot rubber that molds to the shape. I made a shallow score in a scrap piece of letter, and got some decent results cutting up to it with a handheld router.

If the drag knife did work, with a small, 2 head machine they could certainly go to town milling these...