I hadn’t given this a great deal of thought yet but now I am getting closer to being able to make chips I thought I better come up with a solution.
Right now my spoil board is a sheet of 18mm MDF sat on top of the worktop my MPCNC is fixed to.
I’ve done some research but, as with a lot of things, there is multiple paths I could take.
Below are the options I am aware of and some of my, uneducated, thoughts on them. I welcome any comments or suggestions from people who know more and have been using one or more of the options.
Screwing the stoke to the spoil board
This seems to be the simplest option but I can see repeated screwing’s weakening the spoil board over time allowing future screws to slip, also putting a screw in could warp the surface slightly in that area making the stock not sit flush.
Masking tape + superglue
My concerns on this would be the tape or glue letting go and ruining the workpiece and damaging the tool.
Regular spaced holes with captive nuts on the underside of the spoil board.
This seems to be used a lot on other machines. I don’t know how well this would work for me as my spoil board is sat flat on a worktop meaning that there isn’t any space to allow bolts to pass through my board. If a bolt were too long it would ground out and start lifting my spoil board.
Cutting the board up into strips and fitting T-Track between them.
Something else I have seen one a lot of other machines. This would be the most expensive option in the first instance as I would need to buy several meters worth of the T-Track. It does have the benefit of allowing small sections of spoil board to be replaced over time rather than having to swap the entire sheet every time it wears out.
Out of all the above options I am starting to lean towards the T-Track as, although its the most expensive option, its seems to be quite flexible in terms of way to clamp and has the added benefit of saving money in the long term when I get to the point of having to replace sections of spoil board.
Please let me know what options you have tried and how you find them.
I’m pretty much at your stage of the build, so this is not based on experience, however I’m going to run with screws.
I came very close to routing tee slots in the board though rather than using aluminium ones, but came to my senses just in time. That would give you lots of flexibility at no cost once you own the router bit.
My Primo uses T nuts in the spoilboard at regular (100mm grid) intervals. it works fine for me. With that, I have few problems with having the stock sit flat. I have had some interference with the router, but only occasionally. Most of the time, I am careful enough to have the hold-downs out of the way. My spoilboard also sits on a flat surface, but I have the base of the T nut pocketed into the spoilboard, so it can sit flat on the surface. I use threaded rod lengths, so I never need to go all the way through the surface underneath.
My LR2 uses T track. Not entirely sure how well that works yet, since I’m only now completing the machine. I anticipate it being good though.
I have used tape and glue, and it works well.
For screwing things down to the spoilboard… I do many through cuts, which go into the spoilboard underneath. After enough cuts, the spoilboard surface isn’t really that flat anymore, so it only has a limited lifespan in the first place. What I’d want to be careful of is that you aren’t going through the spoilboard into the table surface underneath. I don’t use this much, since I often don’t have a “safe” area that I can put a screw through which I won’t either want to keep, with the finished piece, or can guarantee that I won’t cut.
It did occur to me after writing my post that tape does have the benefit of being able to access the whole part without needing to avoid clamps and its the only option that allows a part to be completely cut out of the stock without it becoming loose.
As with every project I do I am probably massively overthinking this and should just ‘have a go’.
Double sided tape. I’ve seen several different kinds recommended.
Superglue and shelf liner
Vacuum table
Plastic brads
Milled t-slots
My recommendation is to hold off on constructing any hold down system. Use wood screws and/or some tape solution with a plan to construct a more sophisticated hold down system after say 100 hours of cutting. Experience is going to be the best teacher of what you like for hold downs, early mistakes can really mess up a spoil board, and if you use your CNC to create your hold down system, you really want to a shake down cruise before using it for something that matters. Note you can use traditional clamps like what would be used threaded inserts or t-tracks with a full-threaded sheet metal screw. You will have to clean up the dimples left by the screws to keep the stock flat.
has the added benefit of saving money in the long term when I get to the point of having to replace sections of spoil board.
You really don’t want to be replacing sections since you will want to face your spoil board to be parallel to the plane of the router (I wouldn’t do this until after some time using the machine either). And there is not much expense in the MDF for spoil boards. My working area is 24" by 32", so I can get six spoil boards out of a 4’ x 8’ sheet of 3/4" MDF. That works out to about $8 per spoil board replacement.
I don’t know how well this would work for me as my spoil board is sat flat on a worktop meaning that there isn’t any space to allow bolts to pass through my board.
Screws don’t need to pass through. Most people use 1/4"-20 inserts. Just purchase an assortment of cap screws, and pick the right length for the clamps you are using and the stock thickness. Most MPCNC machines are constructed in two layers, with a base layer, and the spoil board sitting on top. If your machine is constructed this way, you could add an extra 3/4" of space by using your CNC to mill matching holes in the base layer to allow some of the screw to pass through. But I use inserts and have never needed this kind of feature.
If you end up going with inserts, I did bump in to one idea by one user that I found interesting. Instead of putting the inserts into the spoil board, he put the inserts in the base board and then used the CNC to put matching (a bit oversized) holes in the spoil board. That way when a new spoil board was needed, all he had to do was mill new matching holes. He did not have to rebuild using the salvaged inserts.
I have used tape/glue and screws. I have never have any issues with tape/glue especially good with my small pieces and whole pieces I can’t put screws in.
I you cut a small rabbet in what will be the bottom of the spoil board, you can “mill” your own t-slot and use brass toilet bolts as hold-downs. This just takes a minute running the board on edge through the table saw, but you can do it with a router as well. The bolts come long enough for almost anything I’d try to cut in my Burly, are easy to cut to length, the big head keeps them from turning, and the flatness of the head means you can keep more of the “meat” of the spoil board. Also, most cutting bits will go through them without as much of a problem as when you hit something steel.
One thing to consider is simply drilling and tapping holes into the MDF spoil board. I’ve used tapped MDF to hold furniture together, and if you don’t tell the engineers around here, it’s pretty quick to do with a tap on a drill.
I can’t see the point in all of those brass inserts no I think about it. You could even use nylon bolts, they are cheap enough as well. If I’m way off please let me know!
Wood taps do work, and these days I actually use metal taps, but in MDF when I was too tight to actually buy gear I’d rarely use (like a tap nad die set) I made my own out of bolts with a sort of wedge shape filed out of the lead thread.
Tape is actually really good in shear, so as long as you apply some downward pressure you’re good (screws, etc.). Another plus for spoilboard solutions is they allow you to mill for flatness prior to cutting.
That would give you lots of flexibility at no cost once you own the router bit.