Feedrate vs RPM Material Settings

[Wisker]

Hello,
I have gotten my Zenbot 4896 all up and running and learned allot in the last month on it and Mach etc. I have run 5 sheets of 3/4 MDF and have had good results with the cuts but i' m not sure it's been done efficiently. So if anyone can lend some advice on settings i would much appreciate it on cutting. I got 5 sheets cut and the bit looked black and bottom?

MDF/Melamine 3/4"- Cut ok but had a high pitch noise when cutting
Baltic Birch Plywood 3/4"- Steps skipped using these settings replaced bit helped

My current settings:
M12vc Hitache Router running 15000 RPM
Amana .250 Compression Spiral Bit
Feedrate Set 200IPM

I run 3 passe on the cut threws.

thanks

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[Wisker]

http://www.woodworkingcanada.com//ho...Calculator.xls

Found a Calculator for types material etc. can anyone look at it and tell if its somewhat accurate? Enter info in yellow areas and it gives feedrate.

[ger21]

High pitched screaming will usually indicate that the feedrate is too low.
Unfortunately, if your machine is losing steps at 100ipm with a 1/4" depth of cut, it won't have enough power to get anywhere close to a manufacturers recommended chip load.

At 15,000 rpm, you should be cutting closer to 200ipm in baltic birch, and maybe 250-300ipm in MDF. This is to maximize tool life.
Many hobby grade machines will have to cut at lower than optimal rates, due to lack of power and rigidity.

[Jim Dawson]

Depending on the total length of all the cutting that you did, you may have just worn out the bit. They don't last forever. Also if you are plunging with a downcut bit, it will burn it's way through. You have to ramp into the plunge. The exception to this is a downcut plunge bit, but it's still better to ramp in if you can. It is also possible that you are not able to get the chip load up high enough so the bit is doing more rubbing than cutting. Try reducing the spindle speed and see what happens, try 8000 RPM and leave the feed at 100 IPM. Reduce the depth of cut if you need to. Go down to your local Home Depot or Lowes and pick up a couple solid carbide Diablo or Bosch bits. They have both up cut and down cut, about $20.

[Wisker]

High pitched screaming will usually indicate that the feedrate is too low.
Unfortunately, if your machine is losing steps at 100ipm with a 1/4" depth of cut, it won't have enough power to get anywhere close to a manufacturers recommended chip load.

At 15,000 rpm, you should be cutting closer to 200ipm in baltic birch, and maybe 250-300ipm in MDF. This is to maximize tool life.
Many hobby grade machines will have to cut at lower than optimal rates, due to lack of power and rigidity.

Sorry i was incorrect on my Feedrate, it originally was set at 100ipm when i received it but i had bumped it up to 200ipm after our previous discussions. So i am running at 200IPM at the moment using a .250 47160 Amana Compression Spiral Plunge bit and i am cutting 3/4 MDF and trying to cut 3/4 Birch Plywood. It was cutting clean smooth cuts at 200IPM on the MDF but had a slight scream so i will bump up the feedrate when cutting the MDF to 250 then 300IPM to see how that works, so do i increase the Feedrate until there is no scream and the cnc isnt missing any steps? I will also setup to ramp into the cuts, I did inspect the previous bit and noticed a chunk out of one the flutes, not sure how or when that happened but im wondering if that caused the cnc to miss steps when i switched to the Birch plywood and tried to cut it, i switched the bit in the middle of cutting the Birch after i watched it stutter knowing steps where know going to be messed up and after starting it with new bit it never missed a step, i did get the scream still only know and then not a constant scream. As far as the RPM on the router it seems to be cutting fairly easy it doesnt act as if there is a load on it or it slows down when cutting, should i leave it at that 15k rpm and try feedrates or should i bump the RPM up as well? The router has 6 settings if they are correct.
#1 = 8,800 RPM's
#2 = 11,250
#3 = 14,650
#4 = 17,500
#5 = 20,500
#6 = 24,500

Thanks for the help, i got allot learned in the month or so i have owned a CNC and looking forward to getting it set so i can start making some cabinets. I will try to make a video of a cut and provide a link to Youtube this weekend so maybe someone can hear and see how it is cutting.

[ger21]

Cutting forces should not be able to cause lost steps. Sounds like your machine is severely underpowered.
At the speeds you're running at, you don't want to increase the rpm any higher.

[Wisker]

Under power do you mean the stepper motors? With a new bit and running at 15k rpm and 200IPM on Birch i am getting good cuts, it is still making the scream noise only know and then, this system is belt driven and i rechecked and tightened all the belts. Can i increase the IPM and leave the RPM where it is at until the scream is no more and i am not loosing any steps? Generally speaking do you set RPM at a set range then adjust IPM or vice versa?

Also could i make multiple passes or is it better to cut in a single or 2 passes when going through 3/4 birch? On MDF im doing 3 passes on through cuts is that not good?

Thanks