Chip load calculators number?

[jzarski1]

Hey all went to use the chip load calc today and got a crazy number. Well at least I think it's crazy.

Using onsrud 60-111 .25" compression bit.
21000 RPM (single speed PC)
.014 for chip load (off onsrud website)

Told me to run at 9.8ips. Is this right? Can I run a PRT Alpha at 9.8ips?

Thanks for the help.

John

[paul_z]

John,

Is it possible to cut at 10"/sec on a PRT Alpha? Yes it is ... but perhaps not wise.

If the cuts are straight lines try 4"/sec. If they are curved, you might want to go a bit slower.

If the finish of the cut is important, cut at medium speed (maybe 3" per sec) with an allowance of 0.040". Make sure your first pass is deeper than the up spiral part of the bit. Then make a full depth pass at perhaps 2" per sec with zero allowance.

Paul Z

[pkirby]

John,
When I get a feed rate from the calculator that I think is unreasonable, I then adjust the RPM to get the feed rate where I want it. So for your application, just lower the RPM to 10,000 and your new feed rate would be 4.6 IPS for a 0.014" chipload.

[jzarski1]

John,
When I get a feed rate from the calculator that I think is unreasonable, I then adjust the RPM to get the feed rate where I want it. So for your application, just lower the RPM to 10,000 and your new feed rate would be 4.6 IPS for a 0.014" chipload.

I can't because I have a single speed PC on the machine. It runs at 21000RPM. I tried cutting today at 4.9ips and it was screaming. Cuts where great just LOUD. Gonna bump it up a bit tomorrow, maybe 5.5ips. See where that gets me. Really not a fan of this single speed PC. it's tempting to put my spindle on the alpha and the PC on the standard. Just don't want to rewire all of it.

John

[paul_z]

John,

Maybe something like this? http://www.rockler.com/product.cfm?page=10760

Paul Z

[jzarski1]

John,

Maybe something like this? http://www.rockler.com/product.cfm?page=10760

Paul Z

Hey Paul,

I have one of those and I tried it but it didn't give me any change. It was either off or on. No matter where the dial was, it would either be off at the lower speed settings or turn on full RPM towards the higher setting. Kinda didn't understand why it was doing that. I was thinking the motor can't do the varying voltage. Any ideas? Would be nice to adjust that RPM even if it's just a few thousand RPMs down that would help.

John

[adrianm]

It says it won't work with a soft start router. Is yours one of those?

[jzarski1]

It says it won't work with a soft start router. Is yours one of those?

Sure is..... Figures right.

John

[Brady Watson]

You should really dump that router for a PC7518 at the very least. Not being able to change RPM is knuckle dragger stuff. Hook yourself up.

...and don't be really concerned with chipload. Just run it. If it bogs down, increase RPM. If it burns, lower RPM. Cut the parts, collect the cash, Bob's your uncle...

-B

[fernball]

Back to the chip load numbers - when I run your input it is simply 21,000 x .014 which is 294 inches per minute (or 4.9 inches per second). The 60-111 is a single flute.

Unless I'm calculating wrong (which certainly happens, ha). Chipload equals feed rate divided by (RPM x # flutes). So feed rate equals chipload x RPM since you have a single flute.

Then there's Brady's more practical advice, but the chip load numbers give us a good place to start if we're unsure of cutter and material.

[curtiss]

21,000 rpm all the time ? Sounds scary.

Seems a bit fast especially for any bigger bits which may be out of balance... which might then tend to fly across the room.

I would suppose if you put it under enough load it would slow down, but that is a bit like putting the pedal to the medal and using your brakes to control speed of your car.

What is the outside tip speed of a 2" bit at 21,000 RPM's ???

[coryatjohn]

What is the outside tip speed of a 2" bit at 21,000 RPM's ???

About 60mph.

[fernball]

to about 125 miles per hour.

Circumference = 2 x pi x radius

[fernball]

183 feet per second - that's pretty fast!

[coryatjohn]

Oh yea, that doubling thing.

[jzarski1]

Back to the chip load numbers - when I run your input it is simply 21,000 x .014 which is 294 inches per minute (or 4.9 inches per second). The 60-111 is a single flute.

Unless I'm calculating wrong (which certainly happens, ha). Chipload equals feed rate divided by (RPM x # flutes). So feed rate equals chipload x RPM since you have a single flute.

Then there's Brady's more practical advice, but the chip load numbers give us a good place to start if we're unsure of cutter and material.

Dee, thank you for that. You are right. I had it set as 2 flute. Besides that you all are right about the 21000 RPM thing. I was just using what came with the machine when I picked it up. It really isn't that bad. It's really loud but cuts great at 21000 and 5.1ips. I am going to get a different router or spindle but first I need to make sure I want to keep the machine. Using it now while I do some upgrading to my PRT standard. That's a whole different thread I will be starting soon.

John