Spent nearly 4 hours on a piece and it messes up on the last pass

[avetrano (ANTHONY VETRANO)]

Hi Chive

Long post here

Here are a few suggestions and in the order I would do this.

Power up and initialize the machine watch and listen to its movements and sounds.

If you have one of the hand held controllers to jog the machine use it to move the machine around to check for smooth movement of all the axis and listen for any changes in movements or sounds of the motors. You can also do a wiggle test on the connectors while moving the machine with the controller. Cover as much of the travel area as you can. You indicated you were nearing the last portion of your cuts so the longer you move the machine around if there are issues with wiring or connectors you will stress the connectors and you could create the problem again. Usually if any connector is bad it can build heat, how much depends on the depth of the problem but connectors should not be hot to the touch.

Tip
While you are doing this have a bit in the router and travel to the 4 outer corners of your machine and lower the bit to the waste board and mark your corners whit a Sharpe marker for future reference. I used the 1/8" probe rod for this part. These marks will give you a quick reference to the outer most boundaries of your machine when you set up large projects.

Make note of any changes in movement or sound changes and what you were doing to make this change happen (wiggling connectors which one). Don’t stop testing until you have checked all movements and connectors. This testing will help if/when you contact support.

If you have or did not identify any issues while doing the above steps continue to the below step before you contact support.

Go over the machine and check every component and screw and make sure nothing came loose.
Check every wire connection and look for pushed out pins or bad connectors. If you found a connection that identified a problem when testing take it apart and give it a really good look for damaged connector pins.

While checking the structure components and you do find lose bolts for now tighten them and move on to the rest of the machine.

Contact support for help with any problems.

Tramming the machine

This is where you will find many different methods people use to do this but here is how i did my machine.

I used a 8/12 and a 6/8 square that I know is accurate. The numbers are the lengths of the square in inches.
If you followed the assembly instructions on squaring your machine you should check it again now
If there is a change the outer boundary marks you made earlier will be changed slightly.

Check and tension all belts as needed

Check the square of the Y axis to the waste board on both the left and right sides of the machine. Use one or both of the squares you have. Correct any issues by adjusting the mounts on the Y axis on both sides.

Check the Z axis assemble to the waste board. do the left and right side and the forward side on both sides of the assembly. Correct any issues you identify and on this step. You may need to adjust not only the left and right square of the Z assembly to the waste board but the forward square of the Z axis also.

Check the square of the router to the waste board both left and right and forward and rear and correct any issues you identify.

This tramming method is very simple it worked for me.

Questions

What was the actual size of your material before machining?

How did you secure the material to the waste board?

Hope this helps

Anthony

[Chivecraft (Chive)]

Thank you very much for the detailed steps, Anthony!

I’ve cut out about a dozen other mid size (12x12, 12x16, 6x6, etc) pieces and 3 of these pieces so far (14x30) with zero issue - I’m guessing I have close to 25 hours of runtime on the machine so far and it’s been flawless (as far as I’ve been aware)

I’ve been sanding down those weird ridgelines and was unaware of what tramming was, but I do have a couple of trusted blocks I can use. I had been adjusting my stepover to .20 for a 3/4" bowl bit and it still was making the marks, so I just figured it was normal.

I noticed my side belts had lost some tension, so I re-tightened them to where they make a slight snap when raised. I’ve also hit the belts with compressed air but didn’t notice anything stuck in the grooves. I keep the machine in my garage (average is 40F degrees outside) - it’s insulated and sits about 15 degrees warmer than outside.

The machine is still square as far as I can tell - measured corner to corner lengths per a samcraft video I watched.

When moving the gantry back and forth by hand (powered off), I did notice something weird - it will sometimes have small ‘tugs’ of resistance as I’m lightly pulling it towards the wrong or pushing it towards the back. The machine initializes fine, rapid positions to all nodes smoothly without any awkward noises or pauses.

To answer your questions:

1. What was the actual size of your material before machining?
   A: roughly 16"x48"

2. How did you secure the material to the waste board?
   A: I used 5 alligator clips on each side and used one of the 90 degree aligner clips that’s included in the carbide 3d “get a grip” set

[Chivecraft (Chive)]

Thank you very much, @WillAdams!

I had learned what I was doing with the outside contour cut from this hex tray video from the carbide3d youtube channel, but your suggestion seems a lot safer/reliable!

[Chivecraft (Chive)]

Hey Guy,

Thank you for letting me know about the 1 2 3 blocks. They look super handy (and not even for just cnc!)

I responded to @avetrano with my troubleshooting/findings, but nothing seems out of the ordinary. The tray is super massive, but folks are really digging the simplicity of it. Might have to write this one off as a neutrino causing a bitflip

[SLCJedi (Josh Tenny)]

The “tugs” you are feeling are the steppers feeding power to the main board, it powering up for a second, energizing the steppers, then the power draining back out. It is good to remember that a motor turned is a generator. It is best practice to not move the machine fast enough manually that it does that as it has the possibility of damaging the control board. I have started just not moving it by hand at all.

[Chivecraft (Chive)]

I have started just not moving it by hand at all.

Thank you @SLCJedi. This makes sense and I’ll probably put this into practice from now on. The assembly/initialization videos from Kevin B @ carbide3d intsruct you to move it by hand at some point, so I figured it way okay to continue doing so.

[SLCJedi (Josh Tenny)]

If the belts are not attached to the stepper, or the steppers are not plugged into the control board, then you can move it all you want. When assembling a SO3 or SO4, I actually adjust the v-wheels before attaching the belts just so I can move the axis around and make sure movement is tight but smooth before hooking up the belts.

[jwhendy (John Hendy)]

Lots of input on tramming here, but I think the main issue is clearly that the bit went into the piece. You can sand away ridges, but in my experience it’s much harder to put wood back where it was

I think @gdon_2003 is correct on losing steps. @WillAdams , is there any ballpark material removal rate that definitively loses steps? I mean, I know it’ll be particular to the machine, bit, etc… but is there some rule of thumb like: this depth/overlap/feed rate is almost certainly “too much” for a Shapeoko?

I had a very similar experience I shared on this bowl I made, but the cause was quite known. I looked away for about 1 second while holding my shop vac hose close to the bit to help with chips and the machine came around and bumped it. Bye bye

Both of our symptoms seem to align… it’s just a matter of how yours happened, as there’s no obvious cause. It’s interesting that (a) it made it all the way around (why wouldn’t it lose steps early if the cause is overloading the machine?) and (b) after side grain, as I think end grain at least sounds way tougher on my machine.

[WillAdams (William Adams (Carbide 3D))]

The problem here is likely tooling engagement — even a quite conservative cut can result in the machine pulling off course if you cut very deeply engaging a significant percentage of the tooling surfaces.

[jwhendy (John Hendy)]

Guessing there’s no specific way to estimate what constitutes “too much tool engagement”? Like some depth as % of diameter * stepover as % of diameter?

And curious, what would be an example of a “conservative cut” that is also “cut very deeply, engaging a significant portion of tooling surfaces”? I think the only handle left to make it a “conservative” cut is feed rate?

[Tod1d (Tod (with 1 'd'))]

I use a similar formula for estimating optimum chipload. But it’s just depth * width of cut.
If the chart tells me I can cut 0.010 D x 0.300 W, I should also be able to cut 0.300 D x 0.010 W
If I increase the depth to 0.020, I should reduce the Width to 0.150.
Not an exact science by any means, but it get me close.
You also have to consider feedrate. If I reduce WOC by 1/2, I can (almost) double feedrate, up to the elusive maximum chip load.

I think what Will is eluding to with “tool engagement” is the case when your width of cut is greater than the radius of the tool. The extreme example being a fully engaged tool where you’re cutting a slot the same width as the tool.
The suggested remedy is to, rather than slotting, offset your vector by 1.5 x dia of tool and use a pocket path with a shallower depth of cut. i.e. with an 1/8" tool, cut a pocket 3/16" wide. This gives enough space for the chips to clear the pocket, and prevents binding, which could pull your axis out of position.

[DugSms (Doug Sims)]

I assume the 30" dimension is running front to back since your stock was 48" long to begin with. Check your overall length from your zero point to the end of your cut. You may have hit to limits of the cutting area and lost steps there.
I had a similar problem when I was cutting some large circles. It turns out that even if you have 33 inches of cutting space, you don’t have 32 inches of room to cut if you start your zero too far back on the machine.
I had set my piece up and zeroed it just far enough back that the very last movement at the back lost enough steps to make it 1/8" off when it came back around.
I’m not saying this is your problem (especially since you said you’ve already cut some of these), but I thought I would mention it if you hadn’t ruled it out.

[WillAdams (William Adams (Carbide 3D))]

The way to allow such cuts to be done is to prevent tooling engagement from happening where possible — rather than cutting a slot just as narrow as the tool which results in both sides of the tool being engaged, add offset geometry and cut as a pocket down to tab height or the penultimate pass — this almost halves the tool engagement.

Working out high tool engagement strategies is for the folks who have access to CAM software w/ adaptive/trochoidal toolpaths.

[pmbaltzell2 (Pierre E Baltzell)]

This was my first thought. Look at where you set your y zero and I bet you hit the limit and it just cut back into the wood. I’ve done that but it wasn’t on anything as serious as a customer project, it was just a spoil board. The hole spacing got off because it had hit it’s limit. I’m still learning.

[Chivecraft (Chive)]

Thank you all for the feedback and suggestions!

Responding to a couple:

Regarding checking my bounds/limits of the machine in relation to where I was trying to cut, both X and Y dimensions had at least 1.5in of extra movement (was able to jog beyond the piece).

The contour cut on the outside edge was making .02" DoC passes from 0.00 to 0.973", so roughly 48 of 49 passes succeeded without fault. @jwhendy 's situation with the bowl makes me think steps were lost possibly because there was too much bit contact as @WillAdams had hinted at, or it hit something on the piece that caused it to skip.

I ended up fixing the tray by using the spot where the bit jumped into the piece to calculate a new edge. Still need to seal the knot, am liking how it turned out so far. Picture attached - please excuse the puppy pad in the background

[gdon_2003 (Guy Donham)]

Good save. A craftsman makes mistakes but being a craftsman they know how to fix the mistake. Kudos.

I have used table top epoxy to fix some cracks on a mirror frame. I colored the epoxy with black Transtint dye. If you use table top it is rated for different thicknesses. I used MAS table top epoxy which is rated for 1/4" or less. I have also used JB Weld 5 minute epoxy mixed with the same transtint dye. You just have to be quick mixing and coloring because the 5 minute epoxy starts to set up rather quickly. Just make sure whatever you use you mix it thoroughly. The knot will not disappear but becomes a feature.

I also filled the butterfly design with the MAS table top epoxy because it cures overnight.

[Chivecraft (Chive)]

Very cool!!! I’m waiting for some ecopoxy flowcast and some black diamond pigment to get here. Just have to make sure I keep the temperature warm enough for the cure to happen.

[gdon_2003 (Guy Donham)]

If the knot goes all the way through the put some tyvek tape under the bottom. The tyvek tape is available at big box stores. It is used to seal up tyvek house sealing sheathing. The thing about the tyvek is epoxy does not stick to it.

If you are worried about temperature check with the OEM. For the MAS they suggest if it is cold you put the part A in a sink with hot water and let it warm up. So check if that works with your epoxy. Then after getting it poured take it into the house where it is temperature controlled. I would not pour the epoxy in the house because the potential for disaster is too great. If you get a leak it is very hard to stop and inside the house you will make a mess and be persona non gratis with the significant other. Also you might want to make a small dam around the knot with the tyvek tape so while carrying the project the epoxy does not run out around the project.

[Freddy (Alfredo Richardson)]

Opportunity is what could be made of it. Add a different species wood there for the patch. Sorry to hear. These things happen. Good luck!