Circles not perfect

[Shane]

Hi, I have only just starting using my PRS Shopbot but have previously used a CNC Shark Pro Plus and Vectric software.

I converted over a file from Vcarve pro that I have successfully cut out hundreds of times on the CNC Shark but now have encountered issues when trying to cut it on the Shopbot.

I have attached the 3d render to show you the cut and also a picture to show the end resulting problem. The issue is that the small circles are not being cut out perfectly round. They seem to be missing cutting out two opposite edges.

I create these circles using a pocket toolpath, 2mm depth and 16mm diameter. 1/4 inch upcut spiral bit (normally I'd use a down cut but have successfully cut using either style of spiral bit on the Shark).

It does a raster to clear the pocket and I have it set at 90 degrees so it runs along the grain. Profile pass is Last and cut direction is Conventional. Ramp plunge move is 3mm. Feed rate, 50mm/sec, plunge 60mm/sec. 12k RPM.

It seems like where the start and end points of the raster that occurs is not being cut out properly when the machine does the last pass around the circumference.

Do I need to set a pocket allowance? It's just strange that I was able to get perfect circles using the inferior Shark.

Another question, do I need to tell the Shopbot which tool I'm using or does it pull all that information across from the partworks file?

Shane.

[Shane]

Hi Everyone, Problem has now been solved. I saw another thread with a very similar problem. I checked my X & Y motors and found X were both not fully engaged to the rack. I had swapped over X motors to test them out a couple of days ago and mustn't of retightened them properly.

Just performed another test cut and perfect circles were created. Thanks Brady for your advice in the other thread.

Shane.

[srwtlc]

Shane,

Are these the first cuts you've made on the Bot? It looks like you may have some looseness somewhere and are in need of some mechanical adjustments. With the machine turned on and locked in, can you wiggle any axis? If you hang on to the lower end of the router/spindle, can you move it in/out from the gantry? If so, you need to adjust the lower v-bearings of the Y carriage to remove the play. Are all the pinions tightened properly and the motors pushed up into the racks. It looks like when there is a change in direction from x to y or vice versa, there is some play somewhere that allows the cutter to wander. Consult the manual for adjusting these things.

Edited to say: Glad you got that worked out while I was typing this. ;)

[jkaras]

Can you use threadlock to lock the motors in place better. i had to do this about a year ago and it is getting loose again.. Thanks!

-Jason

[ssflyer]

Jason,

Thanks for the post, but the thread is 2 years old, and they found the problem...

As far as Loctite products, I don't use them - I check my machine on a schedule.