What is the frame doing?

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.

@mcmiley

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 -

1174%202

021220086-3_med%202

Thank you

3 Likes

I also agree. The whole purpose of the frame is to hold the Maslow machinery and also whatever you are going to cut. It seems that too much effort has been put into making it some structural piece of a building or furniture.

I plan on putting a 1/2" sheet of OSB on my frame and I am certain that it will be square and will have no trouble with any racking. The cost of a 1/4" or 1/2" sheet of some sort is about $12, in the whole scope of things pretty insignificant for what you get.

I understand wanting everything to be strong and worrying about the repercussions of underbuilding a frame but I think that the modified frame is getting over-designed an overbuilt. When you look at Bar’s original design to the current one there is no comparison.

I agree there is no comparison, that is intentional. Bar’s original design
wasn’t good at holding the motors in position.

we are not doing a folding frame for two reasons.

  1. Bar wanted fixed a-frames
  2. folding legs require a bar between them so that they move at the same time
    (otherwise setting up the machine requires two people

Bar doesn’t think that we need the upper crossmember (he thinks the top beam is
good enough). That means that one long diagonal is not going to be good enough.
A long diagonal is going to require another piece of lumber.

If the machine moves too much, we need either that or have the sheet good
provide structure.

walls don’t need to have something on both sides to keep them from racking.

a standard wall as you describe it actually isn’t considered strong against
racking forces. you should investigate the standards for ‘sheer walls’.

The original Maslow frame was not nearly strong enough, and we are probably
overdoing things a little bit, but I don’t think by much.

As for vibration due to the sled movement, remember how slowly it moves

1 Like

I’m setting up the 80/60 frame all by my onesies as Jack Sparrow wold say. If and when I get to using folding A frames. I specifically don’t want them attached so they can be adjusted independently. There are more non perfectly flat surfaces in the world than perfectly flat surfaces. 4 points tied together on a non flat surface will wobble and rack 100% if the time. It is a question of to what degree. I will guarantee I will set it up by myself - I have to. LOL

Thank you

David,

Can you tell me the dimension of the top rail in length of you new center frame? and the length of the two center vertical pieces please. I have an experiment in mind.

Thank you

1 Like

the top rail is 10’, the crossmembers are 82" the verticals are 34"

see the cut list

cut list.pdf (799 KB)

I think the frame that bar made was fine except for the arms that hold the motors. If we just focus on the long cross member and how to attach it to the previous frame then we could have an easy fix. This could be labeled the beginner frame. Then we could go all out with the superior model that cost a little more for wood and requires some advanced joinery. The second model doesn’t have to fit bar’s original qualifications, but could be for the person that will be doing more with the cnc.

1 Like

We are trying to eliminate the need for CNC parts in the final sled, so that we
can eliminate the temporary frame step entirely (saving a lot of time and
effort)

If we eliminate the plywood parts on the frame, the legs have to be assembed
differently, which leads to a lot of the changes.

Various people have been unhappy with no support between the legs (for reasons
other than the machine not being stiff enough)

so we are trying to make a machine that is much faster and simpler to build than
the original machine.

You are looking at the instructions and thinking that they are complex, but
compared to having to build a temporary frame and wait hours for the CNC cutting
to complete, this is very simple to build

2 Likes

What’s the update. Do we have plans that are completed?

I’m stuck at the bank. After I will be going to get lumber and test a
quick leg / frame change.

You should make a video of the build. I’m sitting on my hands waiting for my cnc, so any little bit I can see is inspiring.

I created a step by step manual of the 80/60 build.

Here:

http://bit.ly/2EJm5PR5

I’m experimenting with the current design and trying to help with the new frame build too.

More to come.

Thank you

The link is dead.try uploading a new link.

Sorry - It’s something with Discourse not cut and pasting it correctly.

I tested it over here -

It’s near the bottom post and working there.

or on front page at :

disciplesofcnc.com

Sorry for the inconvenience

Thank you

Speaking of walls and frames, I’m building my frame integrated with the wall in my garage. I mounted the motors onto blocking attached to existing wall studs, and I ripped the vertical frame 2x4s at 10 degrees to mate with the wall surface as if they’re recessed. The bottom of the frame is only about 12" away from the wall, so it’s a narrow profile compared to the typical frames. I haven’t finished it yet, but I figured the motors will be more rigidly supported this way. And I can still park my car next to it.

2 Likes