In preparation of putting my Maslow together, I am trying to decide on which frame to build. In looking at the new default frame and Bar’s bolt-together design, I noticed something that concerns me quite a bit. Both have a horizontal 2x4 that the motors are mounted on. Having worked with construction lumber a good deal in past woodworking projects (and living in an area where temperature and humidity both vary wildly), I know how badly a 2x4 can warp. This makes me think the relative position of the motors will be unpredictable over any period of time.
Now that I think about it, just about the whole frame is made from materials that are very likely to warp due to this issue, leading to racking/warping of the frame itself. Has anyone noticed this issue who has built one of the newer frames? I’m wondering if I should try to make this out of laminated plywood or even metal to try to prevent this issue?
This has been covered in the forums quite a bit. You can search for information on metal frames made from unistrut, which would give you the best stability. Many people have also replaced the top beam with a piece of unistrut, but left the rest made out of dimensional lumber (myself included) and that solution works well, especially when paired with a reasonably rigid backer board. Warping would also depend on where you store your frame (some have them outside) and/or where you are located geographically.
In my opinion, substituting a piece of unistrut for the 2x4 top beam is the most cost conscious and effective way to upgrade the top beam.
Awesome. Thanks for the suggestion. I just looked through some of the unistrut info and I think I’ll go with your method of just using it for the top bar for now. If I’m having trouble with accuracy dropping when the humidity shifts, I can always rebuild the frame with more unistrut parts later, but I suspect that using it for the top bar will be sufficient.
The top bar is what determins the accuracy of the machine by keeping the motors
at the same distance.
The rest of the frame is only there to hold the top beam and workpiece in place.
If the position of the top beam compared to the workpiece changes, it doesn’t
really hurt much (it moves where zero is on the workpiece, but the workpieces
vary enough that you have to set that anyway). If the top beam moves in and out
compared to the workpiece, it doesn’t hurt much as you have quite a bit of room
to play there (on the order of an inch, if not more)
The only problem warping of other components can cause is not supporting the
workpiece, and resulting in the workpiece getting warped, you don’t want that.
Some people living in very humid areas have had problems with the main 4x8 sheet
of the machine warping. Some have moved to using foam insulation instead.
Warping of the workarea plane can also cause the chain to skip on the motor sprockets. It is important to keep that flat and parallel to the plane of the motor sprockets.
it has to be a fairly significant amount of warp to cause this problem,
remember, you can go from very thin to about an inch without the angle of the
chains causing any problem
A 3" or 4" bow across a 4’x8’ sheet isn’t unusual. I’ve had it happen on my first frame. It’s worth watching for and taking precautions against.
I thought about building a torsion box where the 4x8 sheet goes to help keep it flat, but that adds a ton of work and cost, so I doubt I’ll go that route unless I have issues with the sheet warping. Any idea if someone has tried that already?
I found that a 2x4 on edge across behind the top and bottom of the sheet was sufficient. I did have to pick through the pile at the lumber yard to choose straight ones, though.
I have a box beam strongback that I use for boat building that I’m going to try to use to mount the motors. It’s two 10’ 1x4 ‘common’ boards from HD with 4" luan plywood sides glued and stapled. It’s cheap, simple and strong. Here’s a link where I found the design.