Inconsistent Circles

[robb]

The images attached show a simple set of two circles. the internal is a Pocket and the external is a Profile (with Tabs). As you can see the profile path contains serious glitches. I've run this job several times and each time this occurs. The paths are not parallel despite that there was no tool change and the work-piece is very securely held in place (absolutely no movement at all).

The External path has this weird jump at the start-point of each revolution. I can't sand it out so, on this alone, the job is lost. The Pocket/internal path is also damaged. It leaves a tool mark at the start point of each path and it is creating the damage to the edge as it passes down each revolution. Lost job on this too.

I'm using V-Carve Pro 10.019 and the design is consistent and at maximum magification there are no deviances that would cause the code to produce these problems. This has to be MASSO software (3.44).

I had a conversation with Peter Pasuello about another problem and he told me that MASSO 3.44 does have a glitch and that an update is due. Thank you Peter for your kind help and advice. As always a very valuable asset to MASSO and us CNC obsessives.

When is this going to be addressed as I rely on my CNC for part of my living/earnings? I can't afford to throw away pricey hardwoods.

Happy to provide the G-code or the V-Carve file if requested.

Look forward to a reply. Thanks.

 

[testyourdesign]

@robb

Need to understand details for your machine and the masso settings you're using on each axis. Could also be lost steps caused by your drive settings or power supply load.

What setting did you use for the stepper drivers?

Cheers, Stephen Brown

 

[cncnutz]

Hi Robb,

The most likely cause of the tool mark where the cutter enters the material is tool deflection. I'm not sure about the rest but it is unlikely to be a software issue causing this.

I'm guessing that the cutter is about 3mm and as it enters the flutes are pulling it off to the side as it moves into the material and once the cutting starts it is pulled into correct alignment. The harder the wood he more pronounced the effect. Try using lead in and out if possible or slow the entry speed.

Can you please provide the Gcode file and I will give it a test run and see how it cuts. This will tell where to start looking for the issue.

Cheers Peter

 

[evermech]

@robb

tool deflection is an issue no matter what material you are cutting or how expensive the machine you are using. I've learned to choose my cutting directions carefully, to manipulate the deflection to my advantage. For an inside pocket I would ask for a pocket about .030" smaller than final size and machine an inside circular profile after the pocket to clean up that edge. I would use a circular entry and exit on that pass to get a nice finish.

@cncnutz

maybe someone ( who knows how ) should add a main topic regarding cnc machining teckniques and tricks as there are a lot of people who use Masso and who have limited experience with machining. Just a thought.

Guy

 

[robb]

Hi Folks.

First, thank you Peter, Stephen and Guy for your kind and quick response. I have sent Peter the G-Code as requested by separate mail.

I am not an expert in CNC work. I'm learning but, have to make a living at the same time. Not unusual I'm sure.

I will post the machine details and settings tomorrow when I go to the workshop.

What I can tell you is that I have been making these small coasters for a while and all was okay. I recently updated the MASSO firmware to v3.44 and after that these problems started to occur. That doesn't negate anything you guys have written but, I am experiencing something that didn't happen when using the previous MASSO firmware v3.34.2. I'll keep an open mind about that.

I will adjust lead in values as suggested and I also intend to downgrade MASSO back to the earlier version and check that it does what I claim it does.

Guy made a very good suggestion that more technical detail and 'training' information needs to be made available for people like me. I would certainly appreciate that.

Thanks again

Robb

 

[testyourdesign]

I have operated cnc routers for 18 years. Machine stiffness and cutter stiffness are important issues to review. Stepper Motor and Power Sizing is another issue. That much deflection on a small cutter is unlikely. My guess is you are loosing steps because motors are to small. Has this machine produced the same cuts adequately cuts with a different controller?

It looks like you're using an upward spiral cutter and trying to do it in one operation so you're seeing tear out. Try programming it in two operations leaving 0.1mm for a final finish pass and use a downward spiral cutter for the finish cut.

Please upload photos of your machine and cutter. Please provide documentation for your machine.

Regards, Stephen Brown

 

[cncnutz]

Have done a test run of the Files that Robb provided and as you can see everything is working as it should. Even tested to see it was fit for purpose.

I downgraded to 3.44 that he is using and the results can be seen in the photo's below.

@testyourdesign I have seen cutter deflection cause similar marks at the starting point of the cut where the cutter is small diameter and is plunged fast into stock, but there is clearly something nasty going on with Robbs machine.

I'm going to guess something loose on the X axis causing it to move across because it looks like each pass on the outside toolpath is the same. Looking into the cut you can see what looks like tool marks as it does each pass and they all look the same. Really weird. The left, Top & Bottom look good with even spacing all the way until it gets to the left hand side where the inside has a flat and the outside has that strange notch.

It will be interesting to what the answer is.

Cheers Peter

 

[testyourdesign]

@cncnutz

Cutting solid oak is likely a little more difficult to cut but I agree its not the controller. Things to try

1. Use a separate operation to rough-cut the basic outside shape and inside pocket leaving 0.03 in (0.1mm) for a finishing pass.
   
2. Use a downward spiral tool for finish passes.
   
3. Reduce the load on the cutter during the roughing pass by using "Ramp_Smooth" option with the ramp down value spread over a long distance or a very shallow angle (2 to 5 degrees) to slowly go down into the part over a longer period.
   
4. Lead into the part using ramps instead of plunging down into the part at the start of the cut.
   
5. Try reducing the depth of cut and slowing down the feed rate on heavier cuts so that you minimize the tool deflection and load on the stepper motors.
   

Hardwoods can be difficult to cut if the cutter is not sharp or you are using the wrong feed and speeds. Run a series of tests at different RPM's and feed rates to see if you can improve the quality of your cuts. I uploaded some of the recommended chip load values I used when I programmed production CNC routers a while back. They are a good place to start but you will need to tweak the values based on your machines capabilities.

Cheers, Stephen Brown

 

[robb]

I attach the Axis settings. These were supplied by 3DTek when I purchased the machine last year. The original settings were in metric but, despite I live in the UK I use Imperial measurement. I can't visualise metric. So, I translated the metric settings to Imperial. In fact someone on this Forum sent me the Imperial settinsg and were as close as they could be to my translation.

The machine is an Australian CNC Heavy Mill by 3DTek. I could have imported a larger machine for less money from China but, the Ozzies have an office in the UK and I wanted to have someone who spoke English (well, Australians almost speak English) and someone in support in the same time-zone. So, I paid a little more for that I guess. 3DTek has been very supportive. I am still well inside the 12 months support, parts and labour warranty. I have received free tools, free Wi-Fi keyboard and other bits and pieces I didn't expect so, I have no complaints.

The spindle is 2.2KW air-cooled. The steppers are set to 200 each as per 3DTek settings in the construction manual. You have to build these machines from kit. 3DTek offer two Heavy Mill machines. I have the smaller of the two as my workshop is not very wide and I have a lot of floor standing machines already. There is a whole bunch of information on the 3DTek web site.

Once again I am very grateful for the advice that you folks have given. I hope to be able to return the favour at some time in the future.

The images are photographs (Axis) as my keyboard doesn't have a Print key and CTL+P freezes MASSO.

 

[robb]

Hi Guys,

I've been doing some serious research and I have found the problem causing the out of parallel and damaged circles in my earlier email and images.

I owe everyone and apology for being so crass and not checking the physical possibilities first. The problem was (I'm running some tests right now) the X-axis drive belt. My machine has no screws all axis are driven by belts. When I was breaking down the machine today to search for a possible physical/mechanical cause, I found that the X-axis drive belt had a deformation at one point. I marked it and then manually moved the spindle backwards and forward while watching the belt and motor. There was a definite change in movement as the motor gear ran the belt between the marked positions. it also produced an unusual sound and there was slight resistance to movement at that point. I inspected the belt and it was damaged. I could see the steel wires had become exposed and had deformed the belt. Fortunately, the supplier had sent me lengths of spare belt with the machine so I've cut and fitted the new belt and now I'm running tests. So far, in both Oak and Ash the circles are perfect and parallel. I'll run a few more complex shapes with a pocket and profile path beside each other to make sure I'v cracked it but, I'm pretty sure this was the problem.

However due to the excellent help and advice given by you folks I have learned more and am now taking more care about Lead-in-out, ramps, allowances and finishes. Thank you for that.

Robb

 

[breezy]

Robb,

Bicton Men's Shed owns the larger Heavy Mill, have found it to be a very capable machine. We had the drive pulley come loose on the X axis stepper motor shaft, causing a similar error, in our case each time the Z axis stepped down, the X axis moved to the left several mm resulting in a staircase effect on the left and full depth cut on the right, basically the pulley slipped in one direction only.

Asymmetric lost steps on X axis

I would double check the tightness of your drive pulleys because they do vibrate loose.

Regards,

Arie.

 

[cncnutz]

Glad you got it sorted Robb.

Cheers Peter