Cutting small parts in 1/2" Veneered MDF...

[harryball]

This is just a request for wisdom or experience if you care to share...

I'm cutting 1/2" veneered MDF with a 2 flute 1/8" straight cut bit with a 5/8" CEL. I'm taking 3 passes with a spiraling down cut, i.e. it actually makes 4 trips around the part plunging Z in the entire time.

Chip load seems way off, when I plug in .03 I have to drop to 9000 RPM with 2 flutes to see a suggested 9 ips cutting speed. Using trial and error I arrived at my current 5 ips and 11k RPM. Since this part has long curves and some long runs it does reach full speed. I've successfully cut about 30 parts now and am continuing to tune but on the bit broke while cutting this last test batch. Now... the bit has been well used so I'm considering that as one possible factor.

The dust packs in the cuts. On the first time around it looks good, I'm getting chips... but as I continue to make passes the chips are ground to a fine dust that packs. I'm wondering if the bit was over heating, it was just it's time to go, I'm cutting too fast etc... Before I load a fresh bit in the morning would anyone suggest a different cutting strategy or adjustments?

Otherwise I've been mostly pleased with the results. The parts are being held down on one zone with both feins pulling on it. The dust seals the cut and the spiral down cut seems to work well. The only part I'm not completely happy with yet is the amount of chatter on the curved cuts. I'm making adjustments, slowing to a corner speed of 25 seems to have helped some.


Robert

[beacon14]

If you think the dust in the cuts is a problem one trick I learned with larger bits and cuts much deeper than the bit diameter is to make two passes at each depth, one offset from the actual part by half to three-quarters of the bit diameter. This in effect cuts a wider kerf than the bit which helps clear the dust and keeps the bit from being trapped in a deep canyon where the entire length of the flute is rubbing both sides of the kerf while it re-cuts all the dust from the previous passes.

Not sure how this translates to such a small bit diameter, and of course it takes longer, but it might be worth a try.

[jhicks]

Randall, for starters the nature of the down cut bit drives the dust back down into the cut so I understand you may want that to deliver crisp cut on the veneer edges. A couple suggestions. You could follow the cut with an air compressor nozzle and blow out the dust between passes, or you could use an up cut bit and flip the material over cutting from bottom to top so the veneer doesnt chip.
That MDF does get tough and all that packed dust really can be troublesome. One final suggestion would be a Super O Flute or single flute bit to evacuate more dust with an up cut style.
Check the bit temperature as well as the dust as you cut and after you stop the spindle to get an idea of bit temp. Warm chips/dust is good, warm / hot bit is bad and adjust from there.
If you can get away with it, try a 3/16" O flute and get a more robust bit strength.
Good luck

[harryball]

OK, finished the first "real" batch and delivered them. Check out show an tell later when I get a chance to post a photo.

I ran a 1/4" down cut bit with 1/16" offset about 2/3'd of the way through the material. That ran quickly at 5 ips in a single pass, sort of a roughing pass.

Then I ran at 10k RPM and 4 ips with my 1/8" straight flute bit for all 3 passes. The end result was pretty good. It was enough to keep the path clear for the 1/8" bit and my dust collection cleared most of the upper cut dust but still left dust packed into the bottom 1/8" cut to keep my vac effective.

Thanks for the idea David.

Robert