Compression Bit Education

[ohiolyons]

Hi all I have seen Facebook postings of guys with incredibly large machines putting entire sheets of plywood on and cutting an entire bookcase out of 1 sheet.

They use a compression bit and I tried to do a little research on the proper use of this bit and I'm striking out.

They don't appear to be utilizing leads so I wonder how they start without the spiral up portion of the bit causing tear out at the entry point.

It seems to me that you would have to plunge the bit all the way in, away from the finished edge (leads without ramping) and cut the entire edge all at once.

One website I went to implied multiple passes like a normal end mill. Seems like that first pass is going to do the tear out you are looking to avoid.

Thanks in advance

[Adrian]

Without a lead the first plunge/ramp has to be deep enough to go past the upcut section of the bit. Most cabinet machines cut in a single pass. I always cut 3/4" material in one pass.

[ohiolyons]

Sounds like you confirmed my suspicions Adrian, thanks!!

[Beltramidave]

Without a lead the first plunge/ramp has to be deep enough to go past the upcut section of the bit. Most cabinet machines cut in a single pass. I always cut 3/4" material in one pass.

Adrian,
What size is your spindle? Can you give some feeds and speeds for the tooling you are using? Maybe a screenshot would be easiest. Thanks

[ohiolyons]

So I just created a file that cuts a circle out of 3/4" stock and I was able to incorporate a lead and ramp, Life is good.

Next thing that comes to mind if we are making a 3/4" cut. I assume max RPM on spindle but how much do you slow down your feed rate on the x and y axis as compared to a multiple pass cut?

[ohiolyons]

3 HP spindle

This is a hypothetical project.

I'm just trying to understand the process before I actually need to use this knowledge on a project.

[ohiolyons]

Just found this feed and speed chart on amana website

https://www.amanatool.com/pub/media/pro ... pirals.pdf

Good info

[killersoundz]

So I just created a file that cuts a circle out of 3/4" stock and I was able to incorporate a lead and ramp, Life is good.

Next thing that comes to mind if we are making a 3/4" cut. I assume max RPM on spindle but how much do you slow down your feed rate on the x and y axis as compared to a multiple pass cut?

very wrong thinking....read about chiploads. Depth of cut is irrelevant it's just rpm vs feed rate. most smaller machines should be using the slowest rpm your router or spindle can go for under 100ipm. you want to make chips not fine dust

[dealguy11]

Agree with killersoundz on this. If you're running at max RPM then unless you're cutting at hundreds of inches per minute, you're almost certainly burning up the bit. The Amana feed/speed chart should give some insight into this. Your machine may not be capable of cutting at the ideal speeds and feeds - you'll likely have to experiment to see what works best. But slow the bit down!!

[ger21]

They don't appear to be utilizing leads so I wonder how they start without the spiral up portion of the bit causing tear out at the entry point.

You should always use a lead-in, and ramp in along the lead-in.
That's how I've always done it.

800ipm @ 16,000 rpm for a 1/2" bit and a 15HP spindle.