Deformed Circle Cuts

[Braden]

I am having some issues with my Alpha BT48. I bought this used and I am still learning how to run it, but every circle I cut is coming out warped/off. The imperfection almost looks like it is where the bit enters/exits. My bit is .1563 downcut and the material is 1/4" Home Depot MDF (now painted red). I believe I was at 4"/sec when cutting and had the material held down with screws.

Any advice on how to correct this is greatly appreciated.

Thank you!

[jerry_stanek]

Are you doing a ramp into the work

[jim_vv]

I think your feed rate may be a little too high for that size bit (especially a down cut). The bit may be deflecting. Can you supply more specifics such as cutter part #, feed rate, rpm, and step down?

[Braden]

When I bought the machine the previous owner had quite a few new bits that went with it, unfortunately the bit does not have any numbers or indication as to who made it. I did some research and used my caliper to determine the size and type of bit.

I am setting everything up in Aspire and my settings are:

Bit: .1563
Pass depth:.125
Stepover: .0469 - 30%
Router Speed: 16000
Feed Rate: 3.0 inches/sec
Plunge Rtae: .5

Ramp was also used, smooth was selected and the distance was 2"

Please let me know if I missed anything.

Thank you!

[jim_vv]

Have a look at the chip load calculator in the SB software. For MDF, Onsrud recommends a .003" to .007" chip load for a 5/32" cutter. Your settings (3ips at 16K) would give you a .005" chip which is pretty good. You might try slowing the feed rate down to 2ips and see if that helps. I would also turn off ramping to see if that makes a difference. How big is the circle that you are cutting?

[Braden]

I am glad you confirmed my chip load settings! I had to figure out how to add all of my bits into Aspire and I was concerned I may have been off on something.

I will turn off the ramp and try to slow it down to see if that will help. The circle is 1.11" around.

I am using the MDF as a sample for customers, the real project will need to be cut from 1/4" aluminum (not sure if I will need the ramp for this or not). I have read a lot of posts on cutting the aluminum and will be using the Onsrud bits for it. I thought about outsourcing the cutting, but being able to make my own pieces was why I bought my bot and it has the potential to save me a lot of money to do my own cutting. As of right now I will need to do about 4000 pieces, so I am really hoping to be able to get this nailed down asap.

Thanks again for the help!

[jim_vv]

You will certainly want to ramp into the aluminum. Your feed rates will also need to be slowed waaaaay down. Let us know how it goes.

[bearcat]

Would suggest for the MDF hole, slow down the cut speed to 0.5-0.75 IPS, drop the RPM to maintain the chip load and use a spiral ramp with a pass depth 0.125" for a smooth ID.

Ed

[jim shula]

I was having a similar problem on my old 5'x10' machine. As the bit reached the point where it was entering into the point where it entered the material, it would deflect slightly due to the decreased resistance of entering the kerf. After a little analysis, i found the gear was a little loose on one of the X drive motors. It has two motors driving the X axis. The gear is tightened to the motor with shaft with two set screws which had worked loose allowing slop.

I'm not saying this is your issue, but it was only on circles that I noticed anything was wrong.

[adrianm]

I think Jim is on the right track. From the picture the cut looks very similar to those I've seen on other machines where the issue is always traced back to play in the machine somewhere.

[Braden]

I went through and checked everything, a few somewhat loose items were found but nothing too crazy.

The previous owner of my Buddy did do some self work to the machine so I am also wondering if his tinkering may be adding to my issues. One thing done was he created his own 48" extension and I am not even sure what my table should look like from the factory. I am attaching a few pics of the x motor, if anyone sees anything wrong please let me know.

Also, am I crazy for wanting to cut out almost 4000 pieces from aluminum? I dont have a misting application and would just be using Onsrud bits. I was told that I may just be creating a big issue to run into.

Thanks!

[Joe Porter]

The pinion (round gear) needs to be fully engaged with the gear rack. But, your pinion is already halfway off the motor shaft. Check that there isn't too much slop in the motor bracket to the mounting cross member. The motor mount should be able to pivot, but just barely. You mentioned that someone worked on the table, they may have gotton the v-rail mounts (aluminum extrusions) out of wack. At this pint, you may want to go ahead and replace the pinion gear, just because. I believe if you get everything back in line, your round cuts will improve. I have that same type of machine, I checked a round cut (.75") that I had made recently, all was fine. Good luck, joe

[Joe Porter]

Braden, I went back and looked at your pictures again and noticed that there is no spring in your adjustment screw. My Buddy has a spring loaded motor tensioner. I would check with SB and ask them to look at your pictures and advise. joe

[rb99]

If you zoom in on the 1st and second pics, to me it looks like
-the pinion is worn
-the pinion is not lined up with the rack
-the pinion is only 1/2 on the shaft
-as mentioned not holding on to the rack and could be slipping

[jerry_stanek]

It also looks like the stepper and rack are not perpendicular to one another.