Spoilboard & z-travel

I have read about/watched video on quite a few spoil board setups, but I’m left with a question that I want to answer/understand before deciding how I want my setup.

Does increased spoilboard thickness reduce the z-travel? I’m guessing that there’s some room to compensate with the router mount height, but of course there must be some practical limit.

Put another way, what is the thickest spoilboard you can put on top of the factory spoilboard and still maintain the full height of the z cutting envelope?

If anyone has any insight it would be much appreciated!

The addition of a spoil board reduces your Z height. The real reduction is between the spoil board and the gantry. You could feasibly raise the router but there is still the distance between the spoil board and the bottom of the gantry.

Most people are using a spoil board on top of the factory spoil board. For me it has not affected anything because I am generally working with work that is 1.0" high. If you are going to work on very tall projects the additional spoil board could cause problems. But most projects are cut flat on the table so this would not be an issue.

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Your question is all to familiar. The variables vary from useable bit length to router/spindle choice not to mention the HDZ upgrade.

Here’s what I would suggest to give you a better visual perspective. With no bit installed in your router, and no power to the controller (stock set up).

Manually raise the Z axsis by hand to max travel. Record the max travel height.

Manually lower the Z axis to fully travel by taking note that the V wheels does not exceed the end of its rail (you can go to about the center of the V wheel to the end of the rail … optional). You can remove one or both counter springs to avoid fight the Z axsis from retracting.

Just note that if you do not maintain supporting the Z axsis, the Z assembly will come tumbling down.

Record the max lowered height.

The difference is your max total travel.

You can now use these recorded readings and add the unknowns… like Z axis max or lower travel to top of stock base board, bit length, stock thickness or added spoil board on top of stock base board…

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The way I looked at it was first deciding how thick I wanted the added spoil board (I opted for 3/4"). Then I took my length of Z-travel with my most used bits and subtracted that 3/4". For me, I still have ample travel for my present endeavors.

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On my setup, my spoil board at the same height as the black bed frame angle bracket. The thickest material I am currently attempting to work on is 1.75". This gives me ample room to use Carbide 3D’s 0.25" endmill to do an outside profile through cut and an inside pocket.

I started with a 2" thick stock but found out that I also had to allow for the collet nut to clear the stock and also addition clearance for the bit to clear the holding clamps.

So I band sawed off 0.25" from the stock. I could still have done the project at 2" thick but my design included a 1/8" endmill and that caused a clearance and reach issue.

Heres my design to give you an idea. Looks good in simulation but practical potential issue arrised.

So it also depends on the your project design.

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… and also you have to consider “retract height” in your toolpath so there is room for the bit to withdraw to that height. That is dependent (and somewhat set) to your project’s design.


Let’s be clear that the travel height must be divided by approximately two to account for the length of the endmill stickout from the collet PLUS the safe Z clearing distance. There is approximately 3in travel when you have a 3/4in supplementary wasteboard and the stock Z plate (not the HDZ). While you may be able to pull up the router in the mount, realistically the maximum stock thickness you can mill is about 1 1/2in. Pulling the router up in the mount is not generally recommended as it can affect the precision of your milling. Furthermore, endmill with a cutting length of more than one inch are harder to come by, they increase runoff and deflection (decrease precision) and should be used with caution.

Thanks so much to each of you for the thoughtful replies! Great info there and I’m glad I asked. I was planning on a 3/4” spoilboard with some threaded inserts but I’m reluctant to give up any z travel. I’ll start with 1/4” MDF and see how that goes. I plan to use the ‘blue tape & CA’ hold down method.

FYI one of my applications will be carving topography for architectural models. While these will rarely have a vertical face taller than an inch or so (which for example in an 1/8” = 1’ scale model would represent a 8’ retaining wall) they will often have a total relief change greater than 2”. I will have to work up a system of horizontal slicing if I max out the z.

My thinking now is to just keep the machine as versatile as possible at first and see what works.

Thanks again.

I found that out the hard way and ruin my stock. In Vcarve Pro there is a “safe retract” clearance setting that I set to clear my clamps.

I did not take into account the safe retract value in my total max Z travel. I lost my Z position and my router bit plunged into the stock making a terrible noise. When the bit withdrawn from the stock to the safe retract height setting, it exceeded the physical total travel and lost position.

I never ran into this issue with a 3/4" stock and previous projects because all my projects were less than 1.75" thick.

Lesson learned for next work flow:

  1. Check for total travel plus clearance height.
  2. Useable bit length to avoid bit deflection and/or the addition of several bit passes.
  3. Router collet clearance.

There maybe other criteria but for now I am still developing my work flow check lists.

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FYI, if in the future you go to the HDZ, the travel is basically double so for 3D work, you could carve thicker material.


As @luc.onthego mentioned not to manually lift the Z axis, I did pull my Z up during my initial building of the XXL while deciding on my waste board thickness.

You can use CM to jog the Z axis.

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I’m learning something new here.

3" travel ÷ 2 = 1.5" stock height

Hmm, you got me thinking on this project that I wanted to target a 2" stock with a profile cutout and inside pocket.

I reduced the stock to 1.75" as I found out about clearance issues with the 2" stock, useable bit length stick out and to account for bit deflection.

I ruin the 1.75" stock and about to go for a 2nd attempt. Not wanting a lesson redo I need to reconsider my design thickness.

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Depending on your work holding, you can set very minimal safe z heights, when I am tight on space and clamping material from the side, I run 2.5mm or roughly 1/8" safe z height without issue.

Before I got the HDZ I did a lot of tall jobs, it takes a bit of planning with tool stickout and router positioning, I did have plenty of times where I hit to top limit of travel and destroyed my material too

Curious to know what was the thickest stock you had on a stock Shapeoko setup with 0.75 spoil board doing a full cutout.

Planning on attempting another go at 1.75" stock thickness but hesitating till I full comprehend my setup, bit length, safe retract height, etc.

Hi Gerard & Stu,

I’d be interested in hearing the answer to that question as well. i’m still not sure I understand why it wouldn’t be common practice to mount the router in the ring clamp so that the bottom of the bit is only slightly lower than the bottom of the mounting plate behind the router when it is fully retracted. It seems like with that setup, a 1/4" spoil board, side clamps or CA and blue tape, and a 4" bit (3 1/2" of stick out) you could utilize almost the full depth of the z-travel. I understand concerns about bit deflection, but I assume that a 1/4" dia. bit with shallower passes could be used to minimize it. I may also be cutting some rigid foam in the future, where i think deflection would not be a concern.

Granted I just got my machine up and running last weekend and have made exactly 2 cuts, so perhaps I am missing something obvious.

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