I finally got my new Altmill baseboard and spoilboard done. The Altmill stringers were tapped, the base board was attached to the stringers from the top. The baseboard received inserts to be used to attach the spoil board to the baseboard.
Mill base table with attaching screws not screwed down yet:
The dog holes are on 100 mm centers, they are 20 mm in diameter. The slots are match-fit slots used as an alternative to T Tracks. They are also on 100 mm centers. The front board for upright edge milling shows what the match-fit slots look like. They are basically a dovetail (but somewhat specialized) profile.
Next project will be a trial vacuum table that can be installed on top of the spoilboard when needed.
I never knew what those slots were called. Learn something everyday around here.
Are they pretty strong? Iâve always wondered how strong they are because I like the fact that they can cross. Your table looks versatile with multiple clamping options and a nice vertical section.
They are surprisingly strong but especially on MDF and particle board you can get break-outs.
The secret sauce IMHO is the angle of the slots that distributes the forces sideways rather than straight up and down like on a regular t slot. The first time I saw them at a friends house I said to myself that these will never hold (compared to a metal T track) but my friend took a chunk of wood, slid in a clamp on a table, set the wood sample on the table and tightened things up and said âtry and move itâ âŠ. bloody amazing
Just like with T slots, you can over-tighten things so one needs to keep the limits in mind ⊠but the limits of these slots are not where one expects them to be.
BTW, T tracks that cross are available as well âŠ.
I did some more research on exactly how strong these matchfit slots are and ran into an interesting tidbit. If you clamp a piece of wood onto the slotted table with a matchfit F clamp, you can pretty much reef on the clamp however much you want without breaking out. If however you clamped the wood in such a way that it wasnât sitting in contact with the table (ie the top of the slot) then breakout was much easier. This makes sense when thinking about this. The moral of the story is to be extra careful when you are trying to clamp down a floating object (for example an edge clamp to hold a flat workpiece down.
I still believe that there is plenty of clamping force available, even with MDF, for what we need.
@Jens Correct. If the clamped piece is tight against the slot, the MDF wonât break apart at the screw head as the screw tries to pull out. You are essentially squeezing the MDF and your piece together. The mode of failure would be a plug of MDF that pulls out along with the screw. The shear force that holds that plug in place would be a factor of the screw head diameter, the depth of the slot, and the shear strength of MDF.
Conversely, if your piece is not clamped properly, the only thing keeping your MDF together is, well not much.
I guess it goes without saying that, if you are someone who frequently surfaces their spoilboard, the slots get weaker and weaker over time.
In my early days, I bought the kit with the longer dovetail plastic âboltsâ. Back then, I was still resurfacing my spoil board frequently. I found this system to be too weak quite quickly. I ended up defeating the whole purpose of the system, by making hardwood runners. Clearly, this was silly when a t-track would perform the same function.
Now that I almost never re-surface my spoilboard, I could go back to this system, but since I have the t-track installed, Iâll stick to it.
Very nice looking! Youâve captured and explained exactly what I want to do for my spoil board on the altmill. But Iâm curious, as the slots donât run to the end of the table, how are you getting the Microjig dovetails in there?
You canât see it but on the bottom and right end there is an expanded slot just wide and long enough to be able to âloadâ an insert into. We are talking a mm or so wider on each side for a 35 mm long section.
There is no âloadingâ area on the top because the slots exit and also I canât really reach them. I decided to not put loading slots on the left side because âŠ. well just because
Couple of quick follow up questions about your spoil board; what size pipe are you using for the dog holes that gives you 20mm diameter - is it 1/2â?
Why the odd spacing on the 1st 2 rows of dog holes on the x and y axis? Whatâs the advantage to that?
How far inset are your first row of dog holes in the x and y axis?
Primarily for flexibility when setting up alignment points. As an example, if I wanted to set up a stock piece that was 75 mm in either x or y, it would not hit a dog on one axis because the standard dog holes are 100 mm apart. Note that the second row on both x and y is a standard pattern hole like the rest of the dog holes. It just looks a bit odd since the Matchfit grooves are not cut all the way. I could also have just used 50 mm spacing for the holes of the first row .. or 50mm for the first two holes in the front left corner for smaller stock
That and also because I could
Probably about 30 mm without checking. That was strictly based on being able to physically reach with the spindle along the Y axis and not being too close to the edge of the board on the X axis to have issues with possible break-out from pulling the dogs.
Lastly, this is just one iteration and I might do things differently if it turns out that it needs to be set up differently.
As mentioned in another thread, I am still contemplating how best to add vacuum table capability so things could change.
Jens, I have these same slots on a table saw sled. yes they are strong enough but if you crank on them the will break out no doubt The issue i can see with these on a cnc spoil board is the height of the clamps and the CNC Z cclearing it on moves. Just a thought.
