Sorry, I must have missed this while skimming all the responses but a 4’x8’ backer is still required right? If so does that just get screwed straight to your frame and then the work piece gets screwed to the backer with a piece of foam in the middle? I missed how that whole setup is going to be. With no bottom bar to rest your work piece on how will you hold it in place to screw it? Is it a two person job?
The reason I ask is I’m planning on cutting smaller boards at times and they would just fall through your frame with no backer.
In this design, the backer is no longer structural so it could be replaced by anything that’s 4x8… such as a large sheet of rigid foam insulation. As for the bottom bar, a full sheet would catch the front lips of the “kickers” because they are installed to produce a bit to give you a place to rest the workpiece (or at least that’s what was discussed at one time but the above drawing doesn’t really show that well). For something smaller, you would have to add something to the bottom of the cross brace that extended out the front. Maybe put a couple pieces of wood under bolted under the cross brace that can swivel in and out as you need.
So for a full sheet with a foam backer, you’d either have to use clamps to hold your work piece down or screw all the way back to your frame? If so, this doesn’t work for say a 4’x4’. There isn’t much to support the middle. The previous design had vertical supports in the middle (like a house wall) that allowed for a little more possibilities. In my case, I’ll just use a hard backer that I can screw anything to then use foam as my waste board.
That little lip doesn’t seem like enough to catch all that at the bottom but maybe it is.
This is what it would look like with the optional top brace and verticals
to hold a sheet of foam to it, I would use hot melt glue
the lip of the kickers sticks out just as far as the 24 across the front of the original design does. As @madgrizzle says, blocks of 24 of pieces of plywood can be anchored to the bottom of the center crossmember (I would make one of my first projects be a 79" piece of plywood with slots cut in it, screw threaded studs into the bottom of the crossmember, and have some knobs on them to make it easy to adjust)
The bottom is easy, you can make the thing attached to the bottom crossmember a
L profile
for the sides, it depends what you use for your wasteboard. If it’s plywood,
screw blocks to the back of it and attach a 3" or so strip of the same material
to the blocks to extend the wasteboard (the same thing I would do with the old
frame design.
If it’s foam, it’s a bit harder.
Who has tried to cut to the outer edge? how close can you get before the router
has problems? (the chains will help, so it’s possible that we may be able to get
all the way to the edge, at least near the top)
Apologies if I’m beating a dead horse (I know gussets have been mentioned a few times). I understand that we are trying to get away from using plywood, but some amount of plywood has to be bought for the sled. If we lay the top beam on the front leg, using the factory edge to keep square:
I think the key thing that we’re not agreeing on is that the hole the bolt passes through doesn’t matter. The hole could be 1/4 inch larger than the bolt if you want so that alignment there is not critical. In fact the holes HAVE to be too big to account for the human error of the person who is building the frame.
Imagine the case where the holes are 1/4 inch too big and the bolt hangs loose as shown in the picture. As the nut is tightened the bolt essentially becomes shorter and pulls itself into true.
The second strength with the technique on the left is what you pointed out which is that the motor will always mount in the right plane. We’ve seen chain skip issues happen when flex in the old system would cause the sprockets to leave alignment with the chains. By not making this a user defined angle we can make it consistent across all builds and eliminate that issue.
I added several mods to the stock frame design based on your posts. I added and L bracket between the arms and the plywood back. I also built motor mounts that are adjustable, laterally and vertically. I added the lateral adjustments to adjust the chain position for different thicknesses of the material.
I also installed adjustable wheels on the frame for easy movement in my crowded basement.
Here are some pics of the mods.
@dlang I like the up rights (verticals) you added to your frame in the middle for support. I live north of you near @bar, and humidity does work on the plywood here, so any humid place will have trouble. My old original frame was warping with the plywood backer based frame. Your extra uprights provides a great place to tack down a backer board (if used) to keep that plywood a flat plane, or help to flatten a warped piece flat.
May I ask why you made it adjustable vertically? I certainly understand laterally, but trying to understand the benefit of vertical adjustments. Nice work!
