🌞 New Stock Frame Design 🌞

[dlang]

@madgrizzle

Would it be safe to say that someone could take their stock final frame and achieve the same accuracy improvement that this frame is thought to provide by basically adding a new 2x4 to the side of each existing legs and building the top beam off that? I don’t think the back leg on the stock frame reaches as high as what is shown in the new design, but is that critical?

(This doesn’t address things like eliminating the bottom beam and the wings for the stretchy string and any other stiffeners… just talking about the top beam)

yes, Just about anything that puts a solid 2x4 between the motors will get similar accuracy

[dlang]

@bar

@bar

and removes an entire sheet of plywood from the BOM

Actually that’s not true because you still need to make the sled

but you can make the sled from a 2’ square of plywood

[dlang]

@bar

@apprenticeb Great point, we can at the very least suggest that as an option. The plywood really isnt structural

if you took the plywood off, I would expect the machine to collapse

[dlang]

@bar

The big drawback I’m seeing now when I look at the cut list is that you end up with some extra length on two of the 2x4s. Overall it takes six 10’ 2x4s and removes an entire sheet of plywood from the BOM

here is the cutlist for what we have here

[dlang]

@bar

I am still advocating for this type of design as the stock:

It would require adding some bolts to the kit, but it is dead simple to put together and eliminates the need for the temporary frame entirely

let’s talk about what the differences are.

your version is

1. missing forward facing boards to move the chain tension forward
   simple gap, but it means that you need two more 12" long boards
2. has far less structure (will not stand without the plywood
   • no rear support bar
   • no horizontal or vertical structure behind the plywood
   • nothing to prevent racking other than the plywood
3. support for the plywood other than at the outer edges
   • I think this is a noticeable gap, especially for people in areas with humidity
4. replaces the angled arm with the top beam on top with blocks that you bore through.
   • you show two bocks, but if the front of the top beam is going to be just over 6" out from the front of the frame,
   • you will need 3 on each side.
   • This means that you need 11" long bolts.
   • I’m worried that the stack on the two sides will droop unevenly (non-straight holes in the legs, slop in the holes allowing the bolts to angle a bit more)
   • It’s much harder to put a piece of unistrut on this design, as you have to drill through the side of it (or rotate it sideways, which weakens it)

[dlang]

@akamcfly

What about not going with all 10’ lengths? Four 10s and two 8s?

what is the advantage of going with a mix of lengths?

[akamcfly]

The lumber is priced by the board foot. Fewer board feet, lower cost. Also, fewer scraps lying around after the job is done

[dlang]

Lumber isn’t strictly priced per board-foot, if you get equal amount of board feet in different lengths, both extremely long lengths, and extremely short lengths carry a price premium (at least from the big-box stores)

In any case, that’s just an argument to pack things efficiently, not to buy more boards just to have them shorter.

now, my packing things into 12’ lengths results in two boards that don’t need to be over 10’

cut I don’t see that either cutlist would benefit from more, shorter lengths

(sorry I haven’t had time to add dimensions to these, but the bottom one with two equal lengths is 10’ long, and the top bar is 12’ long)

[dlang]

@bar

I am still advocating for this type of design as the stock:
It would require adding some bolts to the kit, but it is dead simple to put together and eliminates the need for the temporary frame entirely

The version we have been talking about also eliminates the temporary frame entirely. It also eliminates the need for the plywood (you can put whatever you want as a wasteboard there, including foam, and easily change it out)

What is it that you see as more attractive in your version?

[madgrizzle]

@dlang

if you took the plywood off, I would expect the machine to collapse

Looking at the design, I see one bolt at the top of each front legs and two screws at the bottom of each front leg (where the lower cross brace is installed). The top can easily rack and though the two screws at the bottom are better than one, it’s not much. I don’t expect the machine to collapse on its own, but I could see the potential of it happening when trying to get a sheet of 3/4-inch ply on it.

[akamcfly]

The thought was that it wasn’t necessary to only buy boards of a specific length and live with the leftovers.

@bar seemed to have 10’ lengths on the brain. He commented that his cut list had more cull than he wanted.

[madgrizzle]

I personally try to avoid 12-foot lengths because I have a short bed. I feel more comfortable hauling 10-foots…

[bar]

@dlang

What is it that you see as more attractive in your version?

It’s hard to compete on a feature-by-feature basis because my version is just a stripped down minimalist design based on yours. I think that there is value in giving everyone the minimum possible design, and then giving everyone the option to make something more complex if they feel up for it.

I don’t think this is a “one or the other” type of thing. It’s more of a what is the absolute minimum we can build, then offer the option to improve it. Take the current design for example which has spawned a whole host of improved versions. I think having a well documented design like yours out there with assembly instructions written for it also and giving people the choice would be a great thing.

Here are the two designs as I am thinking of them:

To address specific criticisms:

@dlang

will not stand without the plywood

I would expect it to stand well without the plywood. I will build it to test, but while there is nothing to prevent racking the legs would easily stand to with the plywood removed

@dlang

missing forward facing boards to move the chain tension forward

simple gap, but it means that you need two more 12" long boards

Yes, I haven’t quite decided how to do that yet. I keep thinking there is an elegant solution that I haven’t thought of. Two 12" boards would do it, but I’m hoping for something cleaver

@dlang

support for the plywood other than at the outer edges

I think this is a noticeable gap, especially for people in areas with humidity

I don’t have a lot of experience with humidity. Technically the humidity is always high in the NW because it’s always raining but I’ve never experienced any plywood warping. This is a good point and duly noted.

@dlang

replaces the angled arm with the top beam on top with blocks that you bore through.

you show two bocks, but if the front of the top beam is going to be just over 6" out from the front of the frame,
you will need 3 on each side.
This means that you need 11" long bolts.

I actually think this is a big strength. In my testing the bolt-through type of connection here was the strongest and easiest to build. Because all of the surfaces referenced are factory edges it gives a good consistent result regardless of the skill of the person assembling. From my calculations based on measuring my old machine you would want an extra 3/4th inches of distance when cutting 3/4 plywood, so adding a 3rd block would put you over by 3/4th inch. I don’t think this dimensions is critical. I think maybe we are thinking about this connection differently. The bolt is really doing no work other than pulling the blocks together really hard, all the strain passes through the wood. The size of bolt hole doesn’t actually matter, in testing I drilled them all a size too big just to make putting the bolt in easy. Everything was loose until the bolt was tightened, then rock solid.

One last strength of this design is that the edge cuts are never referenced. I try to assume that all hand cuts and measurements are good to within about ±.25 inch which I think is reasonable for someone using a hand saw. If one part were to be made .5 inches longer than another in this design everything will still fit together. Having one leg be 1/2 inch taller than the other would not be ideal, but the distance between the motors will stay constant and the triangular kinematics will not be affected

[madgrizzle]

@bar

I don’t have a lot of experience with humidity. Technically the humidity is always high in the NW because it’s always raining but I’ve never experienced any plywood warping. This is a good point and duly noted.

Down here in the deep south, in the winter, it will be 85 degrees one day, 31 degrees the next day, 70 degrees three days later with rain interspersed throughout. I think this causes some of my problems as well as the fact that I have to store the sheets on edge because my shed is no where big enough to store sheets flat (10x16). If the consensus is that they aren’t needed, I’m fine with not having them in the stock design but maybe add a note that states if you live in an area where plywood is susceptible to warping then to add additional stiffeners at the top and bottom.

[marm]

@bar

I think that there is value in giving everyone the minimum possible design, and then giving everyone the option to make something more complex if they feel up for it.

I agree with bar on this one; there is no reason not to give a person a choice between making a simple frame and a more involved frame.

Personally I plan on using the desing by @dlang and @madgrizzle. If things go well I could be done tomorrow and will hopefully post some pictures. I like the idea that the 3/4 backer is not structurally involved in the frame.

[jwolter]

@marm

I think that there is value in giving everyone the minimum possible design, and then giving everyone the option to make something more complex if they feel up for it.

I like that philosophy, though I would add that we should strive for as much commonality between “stock” designs as practical. That way a user can start with the basic, stripped-down version, then add features as their finances and material availability allow.

[dlang]

@bar

It’s hard to compete on a feature-by-feature basis because my version is just a stripped down minimalist design based on yours. I think that there is value in giving everyone the minimum possible design, and then giving everyone the option to make something more complex if they feel up for it.

I don’t think this is a “one or the other” type of thing. It’s more of a what is the absolute minimum we can build, then offer the option to improve it. Take the current design for example which has spawned a whole host of improved versions. I think having a well documented design like yours out there with assembly instructions written for it also and giving people the choice would be a great thing.

There does need to be one default design. I’ll admit that I’d rather have the default be the stronger one with “you can leave these parts out under those conditions” rather than have the default be the weaker one.

The difference in lumber cost is not much, and I don’t think the difference in assembly or cutting time is very significant either.

CNC machines should be pretty solid, it’s easy for things to go wrong.

@bar

@dlang

will not stand without the plywood

I would expect it to stand well without the plywood. I will build it to test, but while there is nothing to prevent racking the legs would easily stand to with the plywood removed

remember, these legs don’t have the 3.5" wide base, they are narrow side on points (at least until things wear down a bit). If the bolts are very tight, then you have a fair amount of force to prevent racking, but if the bolts are even a little loose (see discussion below, I seem to be replying from the bottom up ) you have almost nothing providing rigidity. the 2’ kickers give someone who trips over the back a LOT of leverage against the bottom beam to loosen the screws there.

I would also expect it to stand fairly well when new. My concern is after it’s aged for a few years and screws/bolts have loosened a little bit, and the plywood has gotten chewed up. Now the person goes to remove the plywood (with the sled hung from the top beam) and the frame comes crashing down.

@bar

@dlang

missing forward facing boards to move the chain tension forward

simple gap, but it means that you need two more 12" long boards

Yes, I haven’t quite decided how to do that yet. I keep thinking there is an elegant solution that I haven’t thought of. Two 12" boards would do it, but I’m hoping for something cleaver

until we define something better, we should include the 12" boards, otherwise we run the risk of specifying boards that are too short to cut them from

Given that these are down low in tripping range, I think they should be something fairly durable, and dirt cheap.

@bar

@dlang

support for the plywood other than at the outer edges

I think this is a noticeable gap, especially for people in areas with humidity

I don’t have a lot of experience with humidity. Technically the humidity is always high in the NW because it’s always raining but I’ve never experienced any plywood warping. This is a good point and duly noted.

This difference drives a lot of things. If we weren’t trying to provide solid support for the plywood out a long ways, we could put the legs closer together, which would make the crossmembers shorter… this has add-on effects, which is part of the reason my alternate2 frame used less lumber than the current alternate 3 frame does. This design has them 83.5" on center while my alternate2 design had them 55.5" on center.

making the design solid without any plywood attached requires a crossmember and diagonals, not complex, but a couple extra steps. I’ll admit I didn’t initially see the point, but the idea of being able to use really cheap sheets of foam as the wasteboard, and doing something like hot glue to attach it to the frame sounds very nice (1/2" foam is weak and flimsy, but at 1.5" (3/4 ply + 1/2" wasteboard is 1.25"), it’s easily strong enough, given this design.

@bar

I actually think this is a big strength. In my testing the bolt-through type of connection here was the strongest and easiest to build. Because all of the surfaces referenced are factory edges it gives a good consistent result regardless of the skill of the person assembling. From my calculations based on measuring my old machine you would want an extra 3/4th inches of distance when cutting 3/4 plywood, so adding a 3rd block would put you over by 3/4th inch. I don’t think this dimensions is critical. I think maybe we are thinking about this connection differently. The bolt is really doing no work other than pulling the blocks together really hard, all the strain passes through the wood. The size of bolt hole doesn’t actually matter, in testing I drilled them all a size too big just to make putting the bolt in easy. Everything was loose until the bolt was tightened, then rock solid.

per our discussion 4 days ago in post 🌞 New Stock Frame Design 🌞 - #197 by bar you said “we want The real answer is around 5.85 inches”

3x 2x4 is only 4.5" (and probably on the low side of that), 2x would be 6" of wood
add a half inch or so for the chain/sprocket to clear the wood.

A large bolt through 4 layers of flat 2x4 and end on through the long side of a 2x4 is very strong, but did you actually glue the right angle joint? or just screw it?

But as I see it, it’s going to have the most variation in the resulting height of the mount, between the question of the exact location of the hole in the top beam and the leg, and the probability that it’s not going to be completely straight is high.

I expect that for most people, they will be able to move the mount up and down by an inch or more while the bolt is loose. Where in this movement everything ends up when the bolt is tight is going to vary based on a huge number of variables.

Bolts also have a tendency to work loose, especially when used to clamp wood and the wood expands and contracts (as the wood expands and the bolt doesn’t move, the wood dents where the bolt rests, then as the wood contracts, the wood that dented doesn’t expand, so the bolt is now loose. In this case, with cheap lumber, the bolt is attaching in the way that is going to move the most.

by comparison, the ‘ugly’ process of taking to factory ends and attaching them at a right angle with glue and a clamp, then driving four screws through it is trivial by comparison (and woodworkers reading this are cringing)

and it’s a lot easier to mount unistrut on top of arms rather than having to drill a large hole in it for a big bolt.

@bar

One last strength of this design is that the edge cuts are never referenced. I try to assume that all hand cuts and measurements are good to within about ±.25 inch which I think is reasonable for someone using a hand saw. If one part were to be made .5 inches longer than another in this design everything will still fit together. Having one leg be 1/2 inch taller than the other would not be ideal, but the distance between the motors will stay constant and the triangular kinematics will not be affected

In my design I reference ends in two places (on three pieces, and the cut list makes these factory ends)

1. on the rear kickers (to make it easy to have them square to the legs)

2. At the top where the forward brackets attach to the legs, both the top of the legs and the rear of the brackets are factory ends to make getting them square easy.

[dlang]

@jwolter

@marm

I think that there is value in giving everyone the minimum possible design, and then giving everyone the option to make something more complex if they feel up for it.

I like that philosophy, though I would add that we should strive for as much commonality between “stock” designs as practical. That way a user can start with the basic, stripped-down version, then add features as their finances and material availability allow.

What ever gets defined as ‘the default frame’ is going to be what the majority of people build, even if there are other designs available. I agree that it makes sense to have some different options (my wheeled alternate2 frame, unistrut top beam, 12’ long top beam, and folding versions for example), but where things are so close, what is the advantage of building the weaker one?

The difference here is in the ballpark of $10-15 (2-3 pieces of 2x4), that’s really not ‘as finances allow’

[dlang]

1.5" foam board is about half the price of the cheapest 3/4 plywood

R-Tech 1-1/2 in. x 4 ft. x 8 ft. R-5.78 Rigid Foam Insulation-320817 - The...

it saves you enough to pay for the extra couple of 2x4s

[blurfl]

@bar

value in giving everyone the minimum possible design

This. Some of these designs would be pretty intimidating for entry-level woodworkers. Bar’s design is simple enough to see all the parts and understand what they do.

On the bolts vs. screws question, drill-screws through 2x4s near the ends often split the board and spoil some of the rigidity. This was visible in at least one of the pictures. Through-bolts avoid that issue.