Using the machine to drill spoilboard / base holes

Hi. Just in the final phases of the 3d-printathon and checking what supplies I need for the table/base.

I am planning to have a 18mm ply base and then a 9 or 18mm MDF spoilboard on top (because those are what I already having lying around… probably going to use the 9mm unless there is a good reason to be much thicker?).

I will add the spoilboard thickness to the leg lengths, so he spoilboard just screws down on top of the base. Now, I planning to put a grid of threaded inserts in the plywood base, and then slightly oversized holes above each insert in the spoilboard. Then bolts for any clamps or whatever will pass through the clamp, through the spoilboard and screw into the inserts. Hopefully that makes sense.

My question is about how I manufacture this. Clearly I could manually measure out and drill all those holes, in the base and spoilboard, but it seems foolish when I will have a CNC machine that can do it much more accurately! However, this would require the router to plunge beyond the spoil depth and 12mm into the base, which is presumably outside the designed range of motion.

How’s best to do this? I could build the machine with shorter legs and then replace them with the longer ones once the drilling is done, but this feels inefficient and will mean essentially building and squaring the machine twice. Or will I simply be able to get a longer bit, or perhaps mount it lower in the collet, to temporarily get the increased depth of cut? Or is it possible to shimmy the router down lower in the mounts (I’ll be using a Makita and the V1engineering 65mm mounts)?


When I made my Primo, I used it to cut the pieces for its own spoilboard.

These pieces were made by using dollar store foam board as a spoilboard, with the pieces clamped down carefully.

I made my spoilboard in 4 pieces for the Primo, each one is the same, holding 24 T nuts in a 6X4 matrix, and they screw down into the machine base. The holes for the T nuts go through, so I needed the waste material, but the dollar store foam board worked well for that, though of course it didn’t last very long. The spoilboard has lasted me a long time, and I really like the modular idea. Most of my projects are only on one or two sections of spoilboard, and I have been able to extend the life of the spoilboard pieces by swapping them around. only a few projects use the whole cut area in my case.

With the Primo, the tip of the router can easily reach the spoilboard, so you can go as deep as your endmill is. I cut 18mm deep holes in my first board, you can see it in my build thread (for instance here: MPCNC Primo Schneewittchen - Oldenburg, Germany - #109 by Tokoloshe).

That’s great to know, thanks Philipp.

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Philipp is likely right that your router will go down far enough to drill your holes. How far the router goes down depends on the tubing and lead screw height of the Z axis. If you have not already cut your tubing, you can increase the length of the tubing by 20mm to compensate for drilling the base board. As long as the leg length remains the same, increasing the Z axis height has minimal impact on the machine’s performance. Personally, I added 50mm to the Z height then made the legs adjustable using three sets of 3D printer spacers. As for adjusting the router in the Makita mount, I just checked, and there is very little play. I might be able to move the router down a few mm.

As for your base board and your spoil board, you need to decide if you will be mounting the legs at the height of the top of the base board or the top of the spoil board. When I upgraded to the Primo from the Burly, I redesigned by system so that the legs mount directly to the base board, and the spoil board floats on top, and matches the X/Y working size. If the spoil board is bigger than the working size, surfacing the spoil board will result in a pit. This pit makes it difficult to work with oversized stock. If you do mount the legs to the base board, you will have to increase the leg height by the thickness of the spoil board to get the working height as specified in the calculator.

I’ve read a couple of places on the forum where the idea of inserts being mounted in the base board instead of the spoil board has been suggested, but I’ve never seen a post indicating this method has been used. I like the idea, but, with each of my spoil boards, I make changes in my insert spacing and placement. If I’d put the inserts in my base board, I’d be stuck with the arrangement unless I wanted to rebuild my machine.

Inserts without flanges tend to pull out. I suggest using t-nuts or inserts with a flange. But flanges introduce a problem in that a pocket is necessary to get the spoil board (or base board) to lay flat. When I did my spoil board (inserts with flanges), I temporarily mounted my spoil, had the CNC cut the holes and the pocket for the flanges, then flipped the spoil board once the inserts were installed. This would be much more difficult to do on the base board. It is possible to use a Forstner bit and a jig (board with a hole) to put the pockets in by hand.

If I was attempting what you are considering, my biggest concern would be getting the holes in the spoil board and the base board to align. I think I would mount the spoil board and then have the CNC cut the holes through the spoil board and the base board at the same time. This would ensure all the holes would align. Since the hole size is for the insert not the machine screw for the insert, the hole in the spoil board will be oversized enough to allow for the machine screws. I’d then put the pockets for the flanges in by hand.

I made a lot of mistakes after I completed my first CNC (Burly), and my spoil board quickly became a war zone. I did not put inserts in the board, and used screws or double-sided tape to mount stock. Sometimes the screws would mount the stock directly, sometimes the screws would mount a clamp that holds the stock. I’m really glad I did not put a lot of effort into that original spoil board. Consider skipping the inserts until you have some time in with your machine. After the first 50 hours of use, you will have a much better idea of the setup that is best for the kinds of projects you do.

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I also rarely used them, to be honest. I switched to screwing workpieces down, now I have a suction table for larger workpieces.

Maybe check out this:

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Thanks Philipp and Robert, that’s really insightful.

Just to clarify a few things:

Like has been suggested, the spoil board will ‘float’ on the base, and I will increase the lengths of the legs by the thickness of the spoil board to compensate.

Also, I’m really not precious about the spoilboard at all, in fact my reasoning by putting any mounting hardware into the base is to allow new spoilboards to be more readily manufactured and replaced. I will cut a couple to size (450x300mm, my cutting area) in advance and then it is a matter of drilling the grid of holes and surfacing.

Finally, like has been suggested, I would drill the spoilboard and base at the same time, whilst clamped together, to ensure good hole alignment.

My plan was to have a grid of holes at 50mm spacing. Where you’ve had to change your insert spacing, were you starting with greater spacing than this? I can’t help but think a 50x50mm grid should cover almost every work piece eventuality (with the option of just using screws into the spoilboard as a last resort), but clearly you guys have much more experience so perhaps I’m being naive.

The base will be 18mm birch plywood and I have had good experience using this style of threaded insert: link. I tend to coat the outside with wood glue prior to insertion. I’ve used these to clamp equipment down to a workbench (e.g. a pillar drill) using M8s with a decent amount of torque and have never had one pull out. Those that have had them pull out - is this because they’ve been used in MDF, perhaps? Oh, and if that’s the type of flanged insert you (Robert) were talking about, I’ve found the flange is so thin (certainly less than 1mm) that torquing the insert down compresses the top ply a little and makes the top flush, so no need to do a counter bore.

I would plan to drill 12 or 13mm deep into the 18mm base, then install probably 12mm deep M5 inserts. I thought I would avoid drilling all the way through, even though that would be easier to use oversize clamping bolts (noting I am using a mostly hollow torsion box underneath), because those holes would allow the base to eventually fill up with dust / chippings. Instead I will ensure I have a range of M5 bolts with different lengths to deal with different work piece thicknesses.

Finally, I envisaged oversized countersinking the four corner holes in the spoilboard MDF, to allow me to use countersunk M5 bolts to fix it to the base. This will allow the top of the bolt head to sit a few mm below the top of the spoilboard, so it is less likely to interfere with the cutting tool.

Sounds like I should oversize the Z-tubes (and presumably lead screw as well?) to allow the option of drilling sufficient depth into the base, to give me flexibility however i plan to use the inserts. As you say, I can build and use the machine initially before committing to a solution.

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That is exactly what i did and it works great!!!
The only issue and modification i had to make was the dust and chips that would end up in the threaded inserts. The inserts were pulled out and drilled completely through the table, careful not to damage the portion the inserts thread into. Reinstalled the inserts and now it is easy to clear any chips and dust straight through. There haven’t been any issues since.

When i built my original LR2 I put threaded inserts all in a nice grid on the spoil board… and never really used them. Just use wood screws to the spoil board now. Makes life SOOO much easier.

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I’ve found the flange is so thin (certainly less than 1mm) that torquing the insert down compresses the top ply a little and makes the top flush, so no need to do a counter bore.

It is good to know this can be done in plywood. I find, in MDF, the threads will strip before they compress the wood enough to bury the flange.

I would plan to drill 12 or 13mm deep into the 18mm base, then install probably 12mm deep M5 inserts.

I would recommend drilling all the way through the 18mm base rather than just 13mm. You can set your base board on some scrap wood. I’d likely use 15mm inserts as well. Your stock will vary in height, and you may use a variety of clamps with different thicknesses. Your 8mm machine screws will come in discrete lengths. The longer inserts and the deeper holes will give you more flexibility with screw length.

Finally, I envisaged oversized countersinking the four corner holes in the spoilboard MDF, to allow me to use countersunk M5 bolts to fix it to the base. This will allow the top of the bolt head to sit a few mm below the top of the spoilboard, so it is less likely to interfere with the cutting tool.

You will likely want to surface your spoil board. I usually get two or three surfacings on my spoil boards before replacing them. The depth of these corner bolts below the top surface will define the maximum surfacing depth of your spoil board. Though I’ve never done it, I’ve considered using nylon bolts for holding down my spoil board. If there is metal in my spoil board, I somehow manage to hit it…especially in the beginning.

If you adjust the squareness of your machine, or the positions of the endstops between your initial spoil board and your replacement spoil board, you may have trouble with placement or alignment with the new spoil board. I remember making changes/adjustments and lots of mistakes in the beginning, but that may just be me.

I ran into this scenario. Unfortunately, after moving my stops, the program to drill the table holes is off. With the holes drilled all the way through the table, I simply ran a small drill bit up from the bottom to mark the locations. Then flipped the spoilboard over and drilled larger holes. Not perfect but worked for me. Just my 2 cents. You can keep the change! :grin:

Ok, thanks all. Looks like I need to think carefully about my mounting strategy. But I can come back to it after building and getting a feel for the machine.

You will never be satisfied. :sweat_smile:

Definitely a slippery slope! Welcome to the asylum… :rofl: