Cutting speeds

[paul60]

using a prt standard and cutting at 1.5-1.7 ips
cutting plywood. what router speed is recommended.
3/8 downspiral bit.
thanks paul

[richards]

Paul,

There's a great chipload calculator that is part of SB3. Click on the Tools menu and you'll find it.

However, to answer your question, at 1.5-ips, 1-flute cutter, 0.015 chipload, you'll need to slow the router/spindle down to 6,000 RPM. Running that slow, even with a spindle, won't give you much torque. I find that I need to run my spindle at least 12,000 RPM, which means that I have to have a move speed of 3-ips with a 1-flute cutter to get a chipload of 0.015.

[paul60]

Hi Mike thanks for the information i am using a 2
flute sprial upcut and downcut what chipload should i be looking for? using courmatt bits milwaukie router
thanks paul

[richards]

Paul, you would have to reduce the speed of your router to about 3,500 RPM if you wanted a chipload of 0.015 and a move speed of 1.7-ips.

At such slow move speeds, a 1-flute cutter will allow your router to work at 2X the RPM, which may still be too slow. That means that your chipload will be smaller than ideal. A smaller chipload will also mean higher heat, which make cause pre-mature failure of the cutter.

With the router set to 10,000 RPM, a 2-flute cutter moving at 1.7-ips will produce a chipload of 0.005 - which is way too fine for most types of wood.

[terryd]

Paul,
I approach the debate on chipload from a different angle. I am only interested in the final product. On many occasion I have run the machine with chiploads numbers way off the scale, in fact I create dust. Generally I start the feed speeds low and crank it up 0.5 inches per second until the FINISH PRODUCT just starts to look rough. I can't count the number of times I use to do the calculations and arrive at the suggested chipload and feed speeds; start the machine and watch the chips fly the correct size and the bit go SNAP !. Bit life may be shortened by using too small a chip load but SNAP! is instant death. Being in the Bahamas with supply issues you would be better off in the long run running slower. FYI depending on the ply I generally run 1/2" carbide upcut spirals from Freud at 3 ips in a single pass. The chipload calculations do NOT factor in cutting depth accurately enough to be considered a rule of thumb when cutting plywood and depending on the composition of the core materials its a long shot its correct. I run a PC router and with the noise it makes, you would think its about to give birth, just absolutely gruesome.

My 2 cents (Canadian)

TerryD

[richards]

Terry is right when he says that the FINISHED PRODUCT determines the correct feed speed and router/spindle RPMs. Unlike some of you lucky 'botters, I cut almost 100% man-made materials (MDF, particle board and plywood). A 0.015 to 0.025 chipload works well with those materials. Also, unlike many of you, I've only literally snapped one cutter. That was a 5/16-inch 2-flute Freud that I had been using for about three hours when it just snapped. Every other cutter has run until it lost its edge. I do tend to watch the AMP meter when I run my spindle. When a cutter starts to draw more than normal amps, I change to a fresh cutter. As others have also noted, the actual feed speed, not the 'dialed in' feed speed is the important number. Very little of my work is complex; it's usually just straight lines. Because of that, I don't have to worry about ramping effects. If I were cutting a lot of arcs, circles, or other curved parts, I would base my cutting speed on my ramping speed (about 2-ips).

My general technique is to ramp down into a cut whenever the material allows and then to move through the cut as fast as the cutter and spindle allow with as large a chipload as the desired finish allows. So far, after cutting mile after mile of parts, that has worked for me.