ridge

[Dave Burtchell]

Hi

We have a CS40 that's been running 40 hours a week. Runs like a champ. We've been having this annoying little problem for some time now and I remember it being covered here before, but I can't remember what the general consensus was.

Here's the problem. The little ridge left on the bottom edge of the cut. Only on double pass parts. It's the thickness of the second pass,(0.050).
We've tried a 1/2" stubby bit and slower feed speeds thinking it was bit deflection, but it remains the same. It's most pronounced on 3/4" mdf and denser plywoods.

Any ideas?

Dave

[Gary Urlacher]

I found the same problem with the 1/2" comp spiral bits I use. What I found is, If you look very close at the bit, it was curved ever so much at the bottom. If I cut into the spoil board by .015", problem solved.


Gary

[Thom Davies]

Hey Guys

Yeah i get the same thing when ever i do 2 passes. I have been meaning to post about it but you bet me to it! LOL I'd love to know what causes it


Cheers

Thom Davies

[Forrest Chapman]

Guys,

This is caused by bit deflection. Machining mdf in a climb cut will fix the issue. For the other materials you don't have a choice at the moment but to run in conventional.

Forrest

[Dave Burtchell]

Forrest,

I'm not convinced it's bit deflection. The ridge is about 25-30 thou wide. If the bit's deflecting into the part on 1st pass by about 1/32", the part should be about 1/16" under-sized. This is not the case. The ridged, or bottom, face is about 1/16" over-sized. Single pass, conventional cut parts are not undersized either. I don't get it.
If it's bit deflection and I climb cut, wouldn't the part end up too big? Besides, we tried a short 1/2" bit at a slow feed rate with no change. I guess I'm missing something here.

More help needed,
Dave

[Will Williamson]

It's not so much that the bit is deflecting Its the wear on the bearings of your Z axis assembly. There is even a small amount of downward deflection of the whole head assembly with the bit being pulled down into the material during a heavy cut. So I would think that the bigger ridge the more your bearings and track are worn

[Dave Burtchell]

Forrest,

Talked to our operator again today. We get the same ridge whether we climb or conventional cut.

Will,

I gave some thought to the worn bearing idea. Our machine is about 4 years old. We keep it clean and check all rails for oil film regularly to make sure the auto oiler is working properly. According to a recent post, Thermwood has never replaced a worn out bearing/ rail assembly on a CS45. Now, I may have read that wrong and it may not apply to a CS40, but I'm pretty sure we're not abusing the machine and our feeds and speeds are reasonable for the material we're cutting. Seeing as how the ridge is the same whether cutting in the x or y direction or whether climb or conventional cutting, I can't see how bearing wear could give that result. Plus, if te bearings are loose, I ought to be able to wiggle the thing by hand by grabbing on to the tool holder. I guess I'm gonna have to unbolt one of the bearings and run it down to it's cutting position and see if there's any slop. Dang, i wish this was a software problem.

Dave

[Jeremy Schiffer]

Dave, I wouldn't go taking anything apart just yet. Our machine is less than a month old and has been doing the ridge thing from the get-go.

[Marius Gouws]

Good Afrternoon
I operate our machine since the first day it arrived in the shop, and it always left a little ridge.(two and a half years ago) I cut all my MDF with a 12.7mm up-down cutter. 32mm MDF I cut with 18mm diamond cutter, and it does the same.
We have 3017mm x 2133mm moving table set-up (C40) and after two and a half years the bearing that connects the table to the lead-screw is worn, but we getting another bearing. What I found is that (for fine work,cutting gears out for a wooden clock) putting a G807 in the beginning of program then the table axis (1) and gantry axis (2) accelerate and de-accelerate much smoother than normal.

[Daniel Vonderheide]

You can verify if it is deflection by compairing the code from the first pass to the code for the cleanup. If the values are the same, you can take it a step further and run the code without any material on the table and stop it at the same points in the first pass and the cleanup pass and verify the part location is the same for both. If this is the case, you have some type of deflection.

[David Hall]

Dave,
As Forrest said, this is deflection.

The deflection is towards the side of the cut creating the heaviest load on the tool.
When the tool is burried in a cut on both sides, the deflection will be towards the part for conventional cut, and away from the part for climb cut.
If the tool is loaded only on one side, (like a part on the edge of a sheet) then the deflection will always be towards the part, regardless of cut direction.

Second pass creates a lighter load on the tool, less deflection, and a ridge.

With all due respect to your operator, may I suggest you recheck his information, and be sure the edges you're checking are from a burried cut.

Regards,
Dave Hall

[jerry johnson]

One thing I have noticed is the ridge seems to be smaller when I am using a new bit. After sharpeinig the up-cut portion of the comprression bit ends up a bit smaller in diameter than the down-cut section of the bit.

[Will Williamson]

What is this G807 about? We run a lot of mohogany carving projects where the line segments are very short and the machine is constantly accelerating and decelerating . I wandering if this G807 code would make a difference

[Marius Gouws]

Good Morning Will
I have discovered this by accident when I download the letter block program from somewhere here at the forums. the prog did not want to work the way it was meant to so I change it a bit, and it works fine now. Now I am not a guru, but what it seems to do is that if you have a G807 in the beginning of the your code the machine axis accelerate and de-accelerate smoother, So when I cut real small part , axis 1 and 2 does not do that sudden movements. Now if you put in a G805 or smaller then it will have an revers affect. The bigger the last digit the slower the acceleration. Maybe someone from Thermwood can tell you more, maybe I am wrong. Like I said in my previous post our bearing on the table is stuffed, and I found by inserting a G80# I get a better cut when cutting small part. If I do not, it looks like I have tried to cut the part myself with a jiggsaw. We are still waiting for the bearing from our dealers in Johannesburg for a couple of months now.
Cheers

[Will Williamson]

Marius Thanks
I talked to tech support yesterday about this G807 but you did a better job discribing the options .


Thermwood tech support
Where can we get a list of the other G code numbers that are not in the manual ?

Thermwood Corporation
Why should anyone have to wait 2 months for a bearing replacement ?