My Build - I blame you lot for this....!

[HiltonSteve]

I have been doing some feed/speed calculations for cutting wood and mdf and found that my feedrates are nowhere near what they need to be to give me the correct chipload, this would explain why my carbide cutters seem to produce a lot of dust in mdf and dull off quite quickly.


Calculation -

Chipload required for MDF with a 6mm cutter = 0.33-0.41
My min spindle speed with Kress 1050 - 10,000rpm
No of flutes on cutter - 3

Feedrate = number of flutes x chipload x rpm

So... feedrate = 3 x 0.33 x 10,000

Feedrate = 9,900 mm/min !!!!

A 2 flute cutter would drop this to 6,600 mm/min, but this is still pretty high.


The problem is my machine only had a max feedrate of 2900mm/min, played with all sorts of settings when i first got it running but that was the best I could get. Feedrates/rapid speeds above that and I got stepper motors stalling and missing steps, but tonight i decided to have another go. So, I switched everything on and found for the first 2-3 mins I could get my feedrates up to 7,000 mm /min but then I started getting stepper problems, kept bringing the values down until the problems went away and guess what the feedrate ended up at.... 2900mm/min!

Took the top off my controller box to see how hot the driver cards were and found that the heatsinks on them were seriously hot, you could only hold your finger on them for 5-10secs. So I decided to do a bit of a cooling mod....

Found a couple of 120mm 12v PC fans and made some mounts for them, fixed them over the top of the driver cards which more or less covered the cards completely and wired them up to a spare 12v supply. (see photo's below)

I now have the motors running at 5,000mm/min without any issues and the driver cards don't even get warm. I did wind it up to 7,500mm/min but to be honest I think its just too fast for the machine, 5,000 looks and feels much more comfortable. The next problem was acceleration and decel, had to wind this up to 1000 mm/sec to get square corners when cutting rectangular pockets. I may have to screw the machine down to the bench now to stop it from throwing itself off!

Now running at these speeds it looks feels much more aggressive, maybe a bit too aggressive but does seem to cut a lot cleaner and a damn site quicker.

Conclusion - Cutting MDF can be a bastard nightmare, it can give you cancer and knackers your cutting tools. Looks like I might steer away from using it too much in the future. But from what I have read most woods are in a similar chipload window so still need similar feedrates to the above, may look at getting some 1 flute cutters so I can reduce the feedrates and see if they are any better.

Anyone else finding the need to run this fast when cutting mdf/wood?