I’ve decided to open a discussion of what is the frame doing?
In short our frame is holding up the motors.
I think the discussion of what frame design to use in other places is a question of for how long?
I see the project as an ever morphing entity. So I have a design I believe will last a year. In that time I expect changes to come and I will probably make a new frame before the year is over.
I live in a house that was built 30 years before records exist in my area. I’m used to things that have to change on a regular basis.
I think the other designs are going towards more of a furniture design. Build once to last a long time.
It depends on what your goals are.
So back to the question at hand. What is the frame doing. It is holding something up.
What do walls do? Hold up a roof.
Here is a link to wall framing -
In a standard lumber hose framed wall. You have plates. The plates are made of studs that are primary strong vertically. 2nd they add rigidity against in and out movement of the wall. the wall framing is inherently week laterally. When wall frame is made, to mode the wall often there is a temporary brace place on a diagonal using the weak side of a stud pinned or fastened at at least tow or more points. To make a wall stronger a permeant diagonal steel brace is inlayed into the lumber, this is beyond the scope of this discussion except to say a diagonal brace provides stability in the 3rd demotion and is a standard building practice.
Te have talked about what the studs are doing, they are fighting vertical crush. What are the plates doing? They are holding the studs by tying them ant horizontal intervals and distributing the forces over there mass on the weak side. They are fighting being crushed by the studs. A wall frame works but being trapped in a rectangular shape that fights lateral racking and is enforce by facing material on the inside and out side, the tying or pinning of the dry wall and exterior siding distribute all latter forces to zero.
If I’ve done my job right, my description along with what a wall frame looks like has explained how a wall frame works.
So our frame is similar to wall frame but instead of a roof we are holding motor up against gravity. We need a frame that will hold up the motors, the sled ( ~40lbs ) the cutting material and fight sag.
Wait where did sag come in? Sag is when you suspend a beam between two points and the distance between the points is great enough the sum of the materials own weigh starts to fail resistance to gravity, resulting in sag. By building a wall type frame and holding it up it will begin to sag. As the sled moves around the cut the shift in weight deforms the frame. Our wall type frame is missing 1 side of facing material, it’s suspended and it’s not brace very well.
What can we do to fix this?
First a diagonal brace on the back side will simulate the Exterior surface adding lots of dimensional stability.
What about using those shorter pieces for diagonal bracing. Reusing scrap is always great when yo can effectively. Remember our diagonal bracing is distributing the load to the entire frame, dissipating over the entire mass. Using small spans is using a small mass. This can intensify pressure locally. Below is a reference picture from a build site. Using a entire 20 ft 2x4 is expensive, there are lots of shorter pieces of lumber on a build site. They don’t use them for this. Why? Two fold - it’s ineffective, it cost more in labor time on a job site and they will reuse the lumber.
OK now we have hashed out why a standard wall type frame. The challenge is to use that frame to attach our work piece and have it hold up the motors. As I see it the wall frame, the top or motor mounts and the work piece need to be in one plane. The temporary attachment of the work brice and a full diagonal make a full wall with a distributed load a front and back and fights sag.
After the fact we have tilt. There is an elegant solution to tilt. It’s called and A frame. It’s one of the oldest building forms and gets it’s name from the fact it has 3 pieces that form to look like the letter A.
A simple form is to use 1 fixed point at the top and a flexible material closer to the bottom to limit how far the 2 sides can move from each other. This is often used in Easels.
If we use 1 member of the A frame to extend the side of the wall frame we cam easily keep it in reference to the working plane and attach a top beam.
I have provided more information below. This is where I want to leave the discussion and open it to designs from other people.
I will reference 1 persons design here that works on these principles.
I’m embarrassed I can’t find the separate thread showing his build.
You can see it in this thread -
The choice of joints greatly effects stability see more about joints here-
Reference material to this article -