What's the most rigid way to join 80/20?

[digits]

Hi guys, I am wondering what's the most rigid way to join together 80/20 profiles?

Looking on the 80/20 website, they seem to use plates/gussets to hold the joints together, wheras the Bosch profile seems to make joints using cast 90 degree angle brackets with little protrusions which seem to align the brackets to the slots.

For ease of construction, I'd like to have my profiles stacked to form 90 degree joints (i.e. N-S beam sits on top of E-W beam) rather than having them butt together in a singe plane, as this doesn't rely on having matched length profiles or square cuts to produce accurately parallel structures. What I am wondering though is whether this will adversely affect rigidity?

What do you guys think?

Cheers.

[jcdillin]

I'm using 8020 in the machine i'm currently building. I've actually used both the gussets and the cast corner peices and both seem to be really good. But overall the gussets i've found to be stronger.

[digits]

Originally Posted by jcdillin I'm using 8020 in the machine i'm currently building. I've actually used both the gussets and the cast corner peices and both seem to be really good. But overall the gussets i've found to be stronger.

Thanks for replying

Am I right in thinking that your design uses a lot of butt-joints then? If so, what did you do to ensure clean cut-ends and how did you accurately match the lenghs of cross members?

I need to build a ladder-type frame with perfectly parallel side pieces, and I am guessing that laying the side-'rails' on top of wider cross members much like rail-track on top of sleepers would allow me to achieve parallelism without any accurate cutting. It wouldn't let me use gussets though, and the structure would be taller than if it were constructed with the cross pieces between the side rails, ladder style.

If I build a ladder-frame that's joined with front and back gusset plates, I suppose I could avoid having the cross-members butting against the side rails, but I would have thought that that would be terrible for rigidity.

[jcdillin]

well I lucked out on my machine and was able to purchase alot of the peices precut so they were already nice and square. The peices that I had to cut I used a mill to make the ends as square as possible.





The pieces I was able to get precut were the sides and all the cross members which made for a very square table. Everything else i've just had to tweak.

[digits]

Thanks for the pictures - they do speak a thousand words! You have a very nice looking machine there! If you don't mind me asking, how long did it take you to bolt it all together, and how hard was it to get those linear-rails lined up?

I had also planned to get as much as possible pre-cut, but I am worried I could end up with +/- 1mm or more variation between cross piceces. I suppose that's shimmable though. I could probably also bolt a few profiles side-by-side onto my mini-mill and mill the ends flat - they don't have to be a precise length, just all the same

Cheers.

[jcdillin]

Thanks it's actually the first pictures i've shown anyone.

Well i've been working on the machine since october, but I only get an hour here and an hour there to work on it. But I would say I have about a weeks straight worth of work in it at this point.

It was really really easy to get the rails lined up, because all the bolts fit into the T slot they are automatically lined up pretty close just by bolting it down. I'm waiting till I get all the axises done before I do the final trimming. As far as the parallel alignment it was a no brainer, they just bolted together and it was done.

Edit: I will say this though, the Y axis was really tough to get aligned right, mainly because they are pretty heavy and it's always just me working on it alone

[jcdillin]

Also another note, don't bother buying their expensive T nuts and bolts, I use standard 5/16" carraige bolts from home depot. I get 100 nuts and bolts for about the same as it costs for 10 T nut and bolts. The heads fit perfectly into the channels and work great.

[digits]

Originally Posted by jcdillin Thanks it's actually the first pictures i've shown anyone. Well i've been working on the machine since october, but I only get an hour here and an hour there to work on it. But I would say I have about a weeks straight worth of work in it at this point. It was really really easy to get the rails lined up, because all the bolts fit into the T slot they are automatically lined up pretty close just by bolting it down. I'm waiting till I get all the axises done before I do the final trimming. As far as the parallel alignment it was a no brainer, they just bolted together and it was done. Edit: I will say this though, the Y axis was really tough to get aligned right, mainly because they are pretty heavy and it's always just me working on it alone

They really are massive rails - what are they - 40mm/1.5" wide? They must add a great deal of strength to the design - I think you've just convinced me that 35mm rails aren't overkill! Cheers!

[jcdillin]

Lol yeah they weight alot but I got them for 2 reasons.

1. I was able to get them cheap off ebay
2. By using them that thick I have no measureable deflection on that axis.

Yeah they are just as wide as the 1515 rail.

[joecnc2006]

Originally Posted by jcdillin Also another note, don't bother buying their expensive T nuts and bolts, I use standard 5/16" carraige bolts from home depot. I get 100 nuts and bolts for about the same as it costs for 10 T nut and bolts. The heads fit perfectly into the channels and work great.

What were the pieces you got? 15/30 example?

[digits]

Originally Posted by jcdillin Lol yeah they weight alot but I got them for 2 reasons. 1. I was able to get them cheap off ebay 2. By using them that thick I have no measureable deflection on that axis. Yeah they are just as wide as the 1515 rail.

1) Please don't rub it in - Ebay UK is useless for anything CNC - my rails/screws/motors will have to be new

2) Even if your frame wasn't perfectly straight before mounting those rails, I'd bet the frame flexed to fit the rails rather than the other way round

[jcdillin]

Originally Posted by joe2000che What were the pieces you got? 15/30 example?

I'm using 1515 1535 and 1545 in my machine