Need help and fast - Cutting 1 1/4" thick acylic and bit keeps breaking.

[landmarksign]

Hello everyone....hope someone can help me and fast because the material is on the table and partially cut already....i i have to get it done fast.

I'm cutting push thru letters from 1.18" (30mm) thick clear acrylic.
I'm hogging out a portion (1" deep) of the material first with a 1/2" - 2 flute bit (1 1/4" cut length)
I'm then following up with a finishing pass using a 3/16" - 1 flute bit (1 1/4" cut length).

But...the 3/16" bit keeps breaking. Broken 4 bits so far. Tends to break mainly when going around corners.

The first successful cut was with the 3/16" bit going at F90 S17500 (but may have slowed it down to around F80 while cutting) - depth of cut 1/2" x 2
The next cut was a fail F80 S17500 - depth of cut 1/2" x 2
The next - fail F70 S17500 - depth of cut 1/2" x 2
The next - fail F50 S17500 - depth of cut 1/4" x 4
The next - tried a different calculation F40 S14000 - cut two of four passes and broke. - depth of cut 1/4" x 4

Could it be the deflection of the bit? Are the RPMs too high/low? Feed rate too fast?

Please help with any ideas/ suggestions. I only have 1 bit left and more on order but they may not arrive in time for the due date of the job.

Thanks
Ryan

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[ger21]

Are they breaking on inside corners? If so, then the bit is probably grabbing in the corners.
How much material is the finishing pass removing?
Is the kerf packed with chips?
Are you conventional, or climb cutting?

[landmarksign]

They are breaking mainly on the outside corners. All the corners of the letters are rounded because they're push thrus.
I'm taking off 0.1" for the finishing pass.
It doesn't appear that there's any buildup of material/chips. I have air and cutting fluid blowing on it while cutting.
I'm climb cutting.

[ger21]

I'd reduce the finishing pass to about .015 -.03.
You're removing way to much material with 0.1"

[landmarksign]

that's what i was starting to think as well gerry, thanks.
unfortunately i can't adjust that on the letters i have partially cut already...so i'm thinking of changing the depth of the cuts down to 1/8" just to get them done...but it's nerve racking only having one bit left. LOL loads of fun!

[ger21]

Use the 3/16 bit to rough cut them to .02 oversize , making maybe 5 passes, then do the full depth finish pass.