workbee deflection Z axis

I realize this post is getting quite old, but having recently gotten into CNC routers, I figured I would chime in with my experience and solutions.

I acquired a Workbee 1000X1000 unit with a 2.2kw spindle and the higher torque motors. Overall this unit is very impressive considering its price point and simple design. I had it built, tested, and ready to cut parts in about 3-4 week's time. This includes having to order a new motion controller and a nearly full redesign of my control box layout. I ended up getting different stepper drivers and therefore needed to add some power supplies onto the board. In the end, I had a very trouble-free, quiet, and what I would consider being a fast machine for the money spent. I have a top speed of 150ipm in any given axis and the way I laid out the machine I have a full 5 inches of usable z-axis!

The problem..... I too noticed a considerable z-axis deflection. This was slowing me down, causing issues with some parts, and really just bothering me. Just cutting air I could see the Z-axis bouncing with some of the G-Code I had loaded! I machined an AR15 80 % lower and this is where it really started to show signs of weakness. While I was able to cut a clean and rather accurate part, it was not without the gritting of teeth. I then cut some small steel parts that caused a lot of chatter and bouncing of the z-axis that really just annoyed me. The part came out fine and usable, but it was time to address the z-axis.....

I set my machine up with a moving axis as per the instructions. I thought it to be a little weird at first seeing as it added a ton of weight for the z-axis motor to have to move and no matter which way it was mounted, it was going to be a pain to remove and work on. I decided the first thing I needed to do was go with a moving spindle type design to reduce the mass that the z-axis motor would have to sling around which should help with some of the bounce and help add a minute amount of rigidity. After doing this I saw where the heart of the problem was as it was now much easier to see where all the deflection was coming from! The V-Groove wheels had quite a bit of movement before the x-axis started to give. It was not as obvious before when there was deflection in the z-axis gantry, the wheels, and eventually the x-axis c-beam. I quickly decided to go to a linear rail mounted z-axis! This is the ticket to a smooth, accurate, and stiff z-axis.

So after getting the linear rails attached and the z-axis sorted out for the spindle gantry, the next area that became obvious where deflection was occurring was in the spindle mount itself. So time to add a second mount. After adding a second mount the z-axis was as stiff and rigid as you could expect! The deflection was now evident in the x-axis bearings and c-beam..... At this point though, the deflection in the z-axis is just about half or less than it was originally and I hadn't really spent too much money. A spindle mount and the linear rails were about $100 or so all in. I figured since I had gone this far I may as well go for broke.

The way I set up my machine, I ended up having an extra 20x80 beam that would have been used for the base of the machine. I decided it would be the perfect tool to use as another rail to stiffen the x-axis gantry deflection. I am mounting it so that it lays flat just above the x-axis gantry. I made a bracket that will connect to the top of the now stationary z-axis gantry with V-Wheels that ride in the slots in what would be the front and back of the Y-axis direction. When the x-axis moves side to side, the beam, independent of the x-axis and z-axis gantries, will act as direct support to reduce flex and deflection from the z-axis forces, and the x-axis motor should only have to move another couple ounces from friction and weight of the added bracket and V-Wheels. Since a picture is worth a thousand words and I have written so much already, some pictures have been attached to hopefully show what I mean. Thanks for your time and I hope everyone is well.

For the edit: I hadn't exactly finished this project when I posted this. I completed it today and am at this point satisfied with the result. The 20x80 beam on the top did its job extremely well; so well in fact that it is now the lower part of the x-axis C-beam that is deflecting now. I do not feel inclined at this point to try and stiffen things any further. The deflection that does occur is about 1/4 or less of what it was originally and it requires some dedication to do it. I feel a cutter running through wood should not have a problem. Metal may still be, but I should at least be able to do it with less bounce and chatter.

One plus to this particular design is that you could use the upper beam as a pre-load system for the z-axis to help in tramming. I did not use it for that purpose and set it so that it was in neutral tension. I have some shims ( feeler gauges ) that I used for that. Anyway, take care everyone and I hope this helps.

 

Great info! Appears to affirm both my general assumptions as well as my simulations, which is nice. Good orientation on the 2080 beam too.

 

Hi, Would you mind to tell me what side of linear rail and block that you use? Thank you, I have the same problem with the z axis about the deflection when it cutting.

 

I just tightened down the wheels and this went away for me. Mine was probably excessive, tho. Not sure what rattled loose (the wheel nuts, I suppose) but the machine was clearly degraded from when I first put it together. Now it seems really good again. I have one wheel that isn't great but I can't get to it unless I pull the x axis off.

 

I'd love to know where you sourced these parts? I am having the same issue on my Build (which also has the same 2.2kw Spindle as yours) and would like to investigate going to linear slides.

 

Here's the parts I found for this mod (no reply from OP above).

• 80mm dia. Spindle Mount x 2
• 500mm HGH15mm Linear Rail with 2 Carriages

Nowhere near under $100 that it was in 2020...

Wondering what would be the best approach to attaching the linear guide rails to the 500 mm C-Beam in an orthogonal fashion? From the pics above it looks like the OP just screwed them into slide-in T-Nuts. Will that be sufficient to center them perfectly parallel and hold, perhaps with some Blue Loctite?

The next part needed is a new ~125mmx125mm mounting plate. Guessing I will need to either drill the 26mmx26mm square 4-hole pattern for the four rail carriages into an Open Builds X-Large C-Beam gantry plate, or fabricate an entirely new plate. Which orientation is best? (Green holes are threaded in my eyeballed sketch here).



I will also have to see what the hole pattern is on the Spindle Mounts when they arrive. Hoping they are 10cm apart and will bolt on to corner holes in the OB plate. If I do have to fabricate a plate, I might consider making it 250mm tall so as to space the two spindle mounts apart and add strength.

Thinking about weight on the Stepper motor, as configured now the motor is moving a 500mm CBeam, the spindle, hoses, dust boot, bit/collet, motor, standoffs, end plates, and spindle mount. If reconfigured, the motor would be moving the plate, carriages, spindle, hoses, and mounts. Would be interesting to weigh these part sets and compare.

The other factor is Z-axis transmission - I'm concerned about the offset (in the "Y" direction per se...) of the anti-backlash nut block on the rear of the plate and the ball screw that runs in the C-Beam channel. With the rail and carriage being 28mm tall ("H" in the below cross section section of carriage on rail) how will I adequately and precisely space the plate away from the rails so as to ensure the screw does not bend?

Any help / thoughts/advice would be appreciated. I have up to about 1/8" of deflection in the Y direction of the bit-tip in the spindle which is not acceptable so something must be done. The ShopBot PRS Alpha I use regularly has a linear slide configuration so this seems like a good idea.

 

@Peter Van Der Walt do you have an idea of how I can determine how many spacers I will need to run between the anti-backlash nut block and the XLarge C-Beam Gantry Plate with the addition of 15mm tall linear slide rails? On your normal Lead 1010 configuration, what is the nominal offset between the center of the lead screw and the gantry plate surface?

Screenshot from Build video shows 3mm spacers + precision shims between the blocks and the plate.

X with two nuts,

Z with anti-backlash. nut block:

 

Ok I like that idea.

You are too fast - I edited my post above and found that the spacers in your build video are 4mm. So I will start there.

 

Do you have a 2D CAD library of parts or only 3D files?

 

Yes thanks for the reminder. I looked at McMaster rails but they are not in the budget right now.

Edit: If Anyone else is looking at this, I think these are the McMaster Part numbers for 15mm slides.

Rails: 6709K33 (460mm) and Carriages: 6709K12. $770 for 4 carriages and two rails.

 

Thank you Rick. Good idea on the blocking. Better dust off my very limited Bridgeport skills...

Here's a visual look down the X axis of a 3D finishing toolpath being cut, showing the deflection. Each "row" along my model surface is a step "up" in Y of a few thousandths (8% of 1/16" dia bit). The "wall" should be straight when I solve this deflection issue.

 

Grainger also has 15mm rails (still $500) but lower-profile.



Make me wonder which would be better in a dusty environment - ball bearings or Frelon sliders? I believe our ShopBot has bearings.

 

Really interested to learn more about your mod – do you have any pictures, drawings, or parts list?

 

Wow thanks for digging out those files and pictures Craig, that is a really smart way to do this mod.

In my shop on my little 30x30" CNC I exclusively do very long 20-48 hour 3D finish carves of plywood where I move a 1/6" dia ball nose bit across the surface side to side along the X axis up/down in Z, and stepping back across the model in very small rows of Y distance. I do the 3D roughing on a ShopBot PRS Alpha with a much larger 1/2" shank bit at ~4"/second - there's no way I can do this with my. machine.

The height of my models can vary from 1" to 8" in Z so I need the maximum possible Z travel I can engineer with the parts I have. And I use a 2.2Kw water cooled spindle to stand up to the long machining times at 24,000 RPM.

I configured the machine with the spindle attached to the bottom of a 500mm C-Beam where the Z motor moves the entire assembly up/down.

I did this for max Z height range (and I have extra vertical height on the side "towers" that I haven't trimmed yet until lI land on a final configuration) but I've discovered that the OB wheel/plate system isn't really sturdy enough in this config, thus the deflection pictured above.

Before I buy all these pricey linear slide parts, I am going to see if I can try to simply rebuild it the way the Lead 1010 is configured, whereby the Z-axis C-Beam is fixed to the X-Axis C-Beams, and the motor moves the plate + spindle.



The question is - if I move the X-beams up so I have around 10" of clearance from the deck, will the bit be able to reach the spoilboard? I recall mocking this up while I was building and determining I'd only be able to have about 5-6 Inches of clearance max (around 3/4 of the height of the spindle, by lowering the spindle down in the mounts as much as possible).

Open to ideas/suggestions from you guys on how to get this done!

 

Thank you Rick. And yes I will manage my expectations. I am really not putting much stress on the bit skimming 3mm off of my models after the 3D roughing (at least I don’t think I am…), but I do need to solve (or drastically lessen) the deflection issue.

 

Hey guys wanted to say thanks for these suggestions. My machine has been reconfigured per Ricks design and is back up and running. It is much stronger built this way, but there is still a smudge of deflection at the lowest position due to the Z clearance.

I’ve done some taller plywood billet 3D carves with great success.

The other day I decided to try a piece of walnut I’ve been saving. Unfortunately, after the first hour, I noticed that on the 3-D finishing pass tool marks are pretty aggressive. Is this deflection due to hardwood. Or is it a dull bit?