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First frame suggestions for working full 4' by 8'?

So my Maslow arrived (woot!) and I have proceeded through the electronics steps. Now on to the frame. I ma new to CNC and DIY so this will be an adventure and also please bear with my newbness.

So, I was looking at the bar bolt frame as my starting point. But, I am hearing that the bottom corners are issues accuracy wise, and that I may need to make some changes if I want to go full 4 by 8 as well.

First thoughts were to
A) Use a unistrut (or equivalent) top 10’ bar, versus 2 by 4.
B) Run it slower in the lower corners
C) Put the sled on some UHWE plastic sheet

For A) it looks like the strut could bolt right in in so far as the frame top bar goes. But, then that would leave a question over best way to attach motors. Thoughts?
For C) Would this work? https://www.amazon.com/dp/B0789Q5HRV/ref=twister_B0789N32QZ?_encoding=UTF8&psc=1 And if so how best to attach to plywood sled. Epoxy of some sort?

Or do I need to consider wider from the get go? To allow the sled some area to coast over as well as fix accuracy in bottom?

UHMW is notoriously hard to adhere to things. Generally you would need to rough up the side you were attempting to glue down with coarse sandpaper and then treat it with a high voltage corona to break up the oxygen bonds, allowing glue to properly adhere to it.
This is why I decided to go with UHMW tape. It costs a bit more and requires you to cut it into strips to fit, but the glue is already applied to the UHMW.

So, I was looking at the bar bolt frame as my starting point. But, I am hearing that the bottom corners are issues accuracy wise, and that I may need to make some changes if I want to go full 4 by 8 as well.

First thoughts were to
A) Use a unistrut (or equivalent) top 10’ bar, versus 2 by 4.

this is as much a long-term stability thing as a direct accuracy thing

B) Run it slower in the lower corners

running slower helps if you are pushing the limits in speed, if you are below
the limit, slower won’t make it more accurate

C) Put the sled on some UHWE plastic sheet

this will help

Or do I need to consider wider from the get go? To allow the sled some area to coast over as well as fix accuracy in bottom?

higher and wider are the best ways to get more accurate and reliable cuts. look
at the spreadsheet for the forces involved with different widths and heights.

David Lang

So, UHMW tape it is then. Thanks. Solves that issue. That bonding process does not sound fun given I do not have a high voltage corona wire, and have no idea what it would potentially out gas (if any thing) even if I did.

Maybe I go the 10’ now, and then see how it does and update later if/when needed. I am not sure that looking at a spread sheet will help, as I would have to understand it first no doubt. Someday sure, today I will be doing good to build the frame and get it all working. Baby steps. :stuck_out_tongue_winking_eye:

Hi @Dave_Antolovich, While unconventional the 80/60 frame is designed to reach the entire 4 x 8 work area.

http://www.indyplanet.us/80/60-frame-manual-1/

Thank you

What about a UGMWPE cutting board as base

https://www.aliexpress.com/item/PLASTIC-cutting-board-UHMWPE-sheet/32370064125.html

3€/kg

Awesome so then 80/60 it is plus uhmw tape.

@Bee: Would there be an advantage to the unistrut top bar on that frame? Or does the T set up pretty much address that?

Cutting board is good find. But, I would need it fast and in small quantity. I did find https://www.amazon.com/Winco-CBWT-1824-Cutting-Board-2-Inch/dp/B001DI5VCA/ref=sr_1_9?s=home-garden&ie=UTF8&qid=1531395788&sr=1-9&keywords=uhmw+cutting+board from amazon, but then there is cutting it and how stable will it be vs plywood sled. So, still thinking tape.

I ended up with 2 top boards with 3 4 x 4 inch spacers. Unistrut will not warp in the same way as wood.

I have a wood sled with bees wax on it. I would like to make a acrylic sled as I like the idea of seeing through it. There is no data that says you get better cuts with slippery polymer under your sled.

The only wrong answer is one that doesn’t work. Dive in and see what works for you.

Thank you

Cutting board is usually HDPE, not UHMW PE, and is often textured to have a non-slip surface. They are both polyethylene, but the UHMW chains are much longer, and have a more slippery surface, while the HDPE tends to be easier to machine.

The aliexpress link uses UHMW, but once again, adhering it to your sled is going to be the tricky part. And making an entire sled from UHMW is not recommended, it is prone to stretching and warping under load. The amazon link is standard HDPE - you can tell by its max temperature; HDPE is 160 °F, UHMW is 200 °F. The amazon board would be easier to stick to things, but also not nearly as slippery as UHMW.

UHMW Sheets… for what it’s worth I’ve adhesive sheets for a similar purpose (not for Maslow) that worked well.
https://www.mcmaster.com/uhmw-polyethylene-sheets. I’ve also used quite a bit of glass tape, more expensive though.