Gantry Upgrade to C-Beam

I started working on a dust shoe design for C-Beam

I cut one of the hole too small and did a quick revise and recut, making a thin ring of leftover material.

I was impressed. I never would have tried to cut this thin of a part in MDF on purpose.
But between my upgrades and a downcut bit it came out beautiful thin ring.


your thin ring looks like a solution in need of a problem!:grinning:


Do you happen to have an easel file shared for that?!.. It’s incredible! :smiley:

Sorry I don’t, I used V-Carve to make them.

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Update. (just some thoughts and observations, mostly notes for myself)

I have been carving oak and mahogany. Last night I was powering through oak with a 1/4" at over 120 inch/min no problem, I probably could have gone much faster. :slight_smile:
I am getting lazy. No longer concerned with tuning the feed and speed for best results as even my generic “ballpark” settings seem to work well.

The project I was doing had a huge toolpath file. Too big for my little table to load into memory.
So I started looking into ways to shrink file size.
The first was to reduce the number of decimal places…
For what I was doing I decided to try limiting it to 2 decimal places (instead of 4). I figured 100th of a mm is more than accurate for a decorative wood carving. But that did get me thinking about resolution and accuracy.

It turns out you want to run micro stepping for smother motion and quieter motors, but you might not want to rely on the added resolution of the “in-between” steps. You want to set up your limits and values based on the single step resolution. In practice this is pretty easy.

The Z axis uses a 8mm screw. 200 steps is a full revolution that moves 8mm. So each step is 0.04mm.
So in calculating depth of cuts just make sure everything is divisible by 0.04mm
I work in metric so this is super easy. Depth of cuts get changed from 6.35 to 6.4 or 6.2 etc.

I use VCarve which is supposed to be able to run a constraint on number values generated for g code, but I am doing something wrong because it is not actually doing it.

You can also set the number of decimal places for each axis in the post processor. And that does work as expected.

I have updated my X axis to also use a 8mm screw. But the Y axis still uses a belt (this lets me have a Y axis longer than 1000mm - which is the longest a 8mm screw can go)

My single step resolution on my Y axis is
3mm per tooth, 20 tooth per pulley, 200 steps per revolution
(3*20)/200 = 0.30 mm/step

Z = 0.04 mm/step
X = 0.04 mm/step
Y = 0.30 mm/step

So the various axis single step resolutions don’t match and don’t divide well into each other. :frowning:

But I found a Gear Ratio 15:1 Planetary Gearbox Nema 23 motor and a 40 tooth pulley that will fit.
3mm per tooth, 20 tooth per pulley, 200 15 steps per revolution
40)/200*15 = 0.04 mm/step

So if I wanted too I could swap out the Y motors (they should fit the same just with some longer standoff bolts and spacers) and pulleys and match the single step resolutions on all axis.

The question is would I want to?

It is nice from a design standpoint but so far I have not noticed any resolution issues with my style of carving.
Of course adding the mechanical gearing would increase the torque significantly on the Y axis, which is much more prone to slipping than the X or Z. But upgrading to a Z controller would also accomplish that with the higher motor current.

This is something to look into. I will need to keep a eye on the carve quality as see if resolution is actually an issues.

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I just encountered and interesting issue with the Y axis.

I have been carving tikis out of scrap pine. Which being so soft really shows the seam where the bit changes direction while spiral cutting the final shape.

So I decide to try making one using a raster carve style instead (back and forth motions) and did it along the Y axis so the faint carve lines would be lost in the grain of the wood.

The carve came out distorted along the Y axis. All the details were thinner in the Y axis direction.
Here is the spiral carve:

Here is the raster carve:

Notice how the raised areas (eyebrows, lips, nose ring) are thinner, but the cut out areas (eye holes) are larger.

Also if you look at the spiral carve all - one half of the face is shifted lower than the other. It is the same positioning error, just showing up in different ways.
I looked at another Tiki I carved earlier and it does not have this error.

So what is going on? I think it is a “Backlash” style of error of some kind.
That is, a consistent error that occurs when the Y axis revers direction. The errors canceling each other out so the overall carve is ok, but the different directions are misaligned.

I could be a mechanical issue in the Y axis:
General backlash in the belt (this would have shown up in earlier carves I think)
It could be the belts are loose and slipping back and forth on the pulley,
A pulley could be loose and slipping back and forth on the shaft

I also made some changes to the system settings that could be causing this:
I upped the cutting speed that could be casing it or making it worse
I reduced the number of decimal points on the output (from 0.0001mm to 0.01mm accuracy)

First step will be to make sure everything is tight and adjusted properly. And see if that makes a difference. But if it is due to the decimal point change? Would that be some kind of rounding error because of the resolution mismatch between the axis, or perhaps a positional error due to multi stepping? (if it is then that may be a good reason to replace the Y axis steppers and pulley with the gear reduction versions)

It is surprising that it got so bad so quick. I need to look at some other carves I made after the decimal point change and see if they have it as well.

A quick fix is to just run the raster in the X axis, so that they Y is only moving in one direction for most of the carve. (If I care about making it line up with he grain I just rotate the object and blank 90 deg.)

It will be interesting to see if I can figure out what is going on. I am betting loose belt or decimal point, either of which is an easy fix.

I had a strange y-axis anomaly that didn’t turn up until I was doing laser engraving…as every little flaw would show up in the laser burns. I had a worn spot on one of my belts that caused strange issues…I didn’t notice when using the spindle…until I went back and checked it out. I would examine the belts, both sides, see if there is an issue.


Good call, there was a squished spot on the belt!

One of the pulleys was loose as well. :unamused:
I had used locktight on the pulley’s set screws, But it still managed to work loose somehow. :confused:

I flipped the bet around so the damaged area was on the far end, outside of the range of this carve. Then re-set the pulley and did a new carve.
Much Better!

A good carve and the raster cut didn’t produce some of the odd wavy surface effect the spiral carve does.

I will have to keep closer tabs on the Pulleys. I really need to replace the stock set screws with a longer Allen screw. They have a bigger hex head so I can torque down on them better.
Or upgrade to the gear reduced motors. Because the motors are higher torque they use larger set screws with a key bar to lock the pulley in place.

I am happy that I was able to spot, identify, trouble shoot and fix the problem so quickly
I think I am finally starting to get the hang of this. :slight_smile:

Moving forward, I am going to change the raster direction of the rough cut to be in the X axis direction. I have always ran it in Y. I am not sure why, probably because that is the default? But I suspect the rough cuts are putting a lot more load on the axis, So minimizing the load on the Y may help prevent things from getting out of alignment in the future.

Also, for the reclaimed pine, I am going to try reducing the machine allowance on the rough cut to see if it will make less fuzzes. I might have to add a second rough operation with the smaller bit.


Update: After living with the upgrade for a few months I can really see a difference in quality between the X axis (anti-backlash thread drive) and the Y axis (belt)

So much so that I now cut with my projects rotated 90 deg so that the bulk of the motion is along the X axis.

I am seriously thinking about upgrading the Y axis to a threaded rod as well.
There are a couple of issues though.
C-Beam only goes up to 1000mm. But I REALLY like the extra cut length the doubled Y length gives me (2000mm). I have yet to use the whole length. But being able to cut on a 4’ x 2’ pre-cut sheet makes life so much easier. I could probably make due with 1500mm (max c-beam length) but threaded 8mm rod really can’t go over 1000mm. So I would have to step up to a 16mm ballscrew setup which can go up to 2000mm.

The thing I am still pondering is, do I stick with my current Y rail at 2000mm? It should be fairly easily to adapt to a ballscrew setup. I may not even need to make new gantry plates.

Or do I switch to a 1500mm ballscrew and c-beam setup? The solid v wheels seem to be holding up better but I would need to design make new gantry plates. (the ballscrew won’t fit on the inside of the c-beam)

If the ball screw rod just “clamped” in place like the threaded rod does I would switch now and just cut down the thread later if I decided to go c-beam. But It doesn’t. The ends are machined for a specific length.

I am strongly leaning toward doing the 2000mm upgrade. Just because it would be simpler to do right now. And later on either replace the rods or deal will joining two 1000mm c-beam rails together.

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So at 8mm acme the size is limited to 1000 mm for flex.
But there are 3 options for long axis.
One is belts :-1:t2: Or much thicker belts.
Two is screws but at that length it’s gonna be huge.15mm maybe?
Three is rack and pinion with controller compensated backlash.
Research and decide how long you truly need it to be before going with a commercial machine.

Search for a post I did on ballscrew upgrade, I posted a link comparing ball and acme screws which emphasized the use cases and was the reason I bought a 2000mm ball screw in 16mm…

My guess was close it seems :grin: 15mm!

I ran a detailed 3D cut last night and had some minor misalignment issues on the Y axis between the rough cut and the final pass.
I didn’t notice it when it happened so I am unsure if it was lost steps, slipping motor or just stretch in the belt. :confused:

I will check the belts and pulleys again, but I am getting fed up with this.

I am reasonably certain that it is not a belt slipping, the G3 is strong. Though it could be a tension issue.
I don’t think it is chip overheat - I have the controller re-posited for better cooling and 2 fans on it (top and bottom)
It could be a pulley, the set screws keep being a problem.
It could be a current issue. I have the pots turned up fairly high, maybe too high?
It could be the motor slipping. (but as I said I have the pot turned up almost as high as they can go.)

I think I need to upgrade the Y axis. I want to do a full upgrade, replaced upgrade everything (Screw drive, V rail, controller, stronger steppers). But I don’t have the $ for all of that.

So I am debating.
Do I go with stronger steppers & external controllers?
Replace the belt with a screw drive?

I think either will be an improvement.

@PhilJohnson seems to have had really good results with his motor / control upgrade. So I am sure I will see an improvement with that.
Upgrading the Y axis motors sees to be the cheaper option. (Simpler too as I don’t need to cut new gantry plates) So I think I will try that first.

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I have 269oz on my Z and X (Dual 140oz on Y) with external (single) drivers set at 2.6A.
I am unable to hold them back :slight_smile:
Using 1/2 step on all axis. (and ACME T8 screws)

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Not to spoil your upgrade plans, but if you are having mechanical issues with the stock system upgrading the motors and drivers will probably not help. Work out the issues and get the machine running properly and then upgrade if you feel it is necessary.

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Yeah, I agree. that is what I have been debating. :confused:
However, I am not running stock anymore. I have upgraded the Y axis / belt drive about as much as I can.
From my “Grab the gantry and shove” tests the weak point seems to be the motor current?
I can still get the stepper to “slip” with a strong tug.
The pots are already just about maxed out, so I think I am getting about as much as I can out of my tinyG controller board.

Upgrading the belts to G3 and having each y motor on it’s own chip (the tinyG has 4) made a huge difference. I used to have a lot of problems unless my cut settings were perfect. It is just annoying when it does it sometimes. Usually when on a complex 3D carve.
(Hmmm, maybe it is an communications issue? It was about 77k lines of gCode. Note to self go over the configuration settings)

Thanks to Phil’s experiences with the separate controllers and new motors I know I will not regret doing it. Even if I still have the same issues I am having now.

A bit more research. My tinyG board is 3.2v which is not enough to trip the 5v inputs on the controllers. (I had the same problem trying to drive a solid state relay for the spindle/dust collector)

I had original intended to just do the Y axis. Taping into the tinyG board (it has solder points already labeled just for that purpose) for the 2 controllers. But that won’t work. So I will have to use the Arduino or get a logic level adaptor module. Which is a shame because I really liked the tinyG multiple workplace coordinate options.

If I do all 4 motor controllers at once I can just used my old Arduino board by itself and not use the gShield at all.

Here is a pin diagram for future reference:

Works like a charm for me aswell :slight_smile:

Note - I needed to feed my Arduino board with a separate 12V source otherwise it would “noise out” when starting a carve. Jogging was fine.
The clone board seen here didnt like 12V input and smoked, replaced it with a genuine Uno and have had zero issues.

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have you check the screws on the stepper pulleys? I thought mine were good and i’d used loctite however on close inspection the X axis pulley we rocking slightly on the flat of the stepper shaft. Not so much it was spinning just moving a little bit when the X axis changed direction.

I replaced the little grub screws with a proper cap head bolt and its like a new machine.

They have been a problem before and I don’t trust them.
I picked up some strong cap style bolts last night to replace the stock set screws.

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