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.

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.

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.

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.


http://www.jcdsystems.net/cnc140.jpg


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.



http://www.jcdsystems.net/cnc142.jpg

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.

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 :D

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.

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 :D

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!

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.

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?

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 :)

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


I'm using 1515 1535 and 1545 in my machine

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 :)


Yeah even here it's hard to find stuff on ebay everyone else bids it up so high that it's hard to afford on my budget.


lol your probably right!

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.

Thanks for sharing. I am ordering 8020 material for a setup I am building. The pic's look great.

Well, having actually played with a shed load of aluminium extrusion and 350 t-nuts, I have learnt a few things, but also have some more questions for those in the know:

All the brand-new extrusions that I have bought (Hepco & Bosch) have been very squarely cut. This has actually made square butt-joints possible, but I still haven't used them much in my design as my gut feeling is that stacking extrusion can give stronger joints.

The cast 90 degree aluminium corner brackets are pretty solid, but they are a pain to use with T-nuts as the nuts rarely want to rotate so that they are perfectly at right-angles to the slots. This has a negative effect on rigidity, so it is very important to get right! The other problem with the cast brackets is that they obviously don't provide any clamping directly where the profiles meet, as they are offset from the joint - which seems to mean that you'll need at least two brackets per joint to achieve any torsional rigidity. Finally, and this is significant IMHO, the brackets are about £10/$20 each with fixing hardware.

What I haven't tried so far is drilling into the profiles - I know they do have fixings that are designed to slide into a T-slot and then be tightened using an allen key via a hole drilled through from the far side of the profile, but what I want to do is to use T-nuts and through bolts to bolt two profiles together with the bolt head on the outside of the profiles for easy adjustment. Has anyone done this, and if so, does drilling holes through the T-slots significantly weaken the profiles? Also has anyone tried drilling through the profile edges/centres, rather than the T-slots - e.g. to mount something with a 1.5" bolt pattern on extrusion with a 1" gap between T-slots?

Cheers.

Well, having actually played with a shed load of aluminium extrusion and 350 t-nuts, I have learnt a few things, but also have some more questions for those in the know:

All the brand-new extrusions that I have bought (Hepco & Bosch) have been very squarely cut. This has actually made square butt-joints possible, but I still haven't used them much in my design as my gut feeling is that stacking extrusion can give stronger joints.

The cast 90 degree aluminium corner brackets are pretty solid, but they are a pain to use with T-nuts as the nuts rarely want to rotate so that they are perfectly at right-angles to the slots. This has a negative effect on rigidity, so it is very important to get right! The other problem with the cast brackets is that they obviously don't provide any clamping directly where the profiles meet, as they are offset from the joint - which seems to mean that you'll need at least two brackets per joint to achieve any torsional rigidity. Finally, and this is significant IMHO, the brackets are about £10/$20 each with fixing hardware.

What I haven't tried so far is drilling into the profiles - I know they do have fixings that are designed to slide into a T-slot and then be tightened using an allen key via a hole drilled through from the far side of the profile, but what I want to do is to use T-nuts and through bolts to bolt two profiles together with the bolt head on the outside of the profiles for easy adjustment. Has anyone done this, and if so, does drilling holes through the T-slots significantly weaken the profiles? Also has anyone tried drilling through the profile edges/centres, rather than the T-slots - e.g. to mount something with a 1.5" bolt pattern on extrusion with a 1" gap between T-slots?

Cheers.

Forget the t-nuts and go with 5/16 carriage bolts. A 1lb bag at Menards goes for about $1.25 for 3/4 to 1 1/2 inch.
Theres plenty in a bag.
I'm using 3mm x 3inch x 5inch steel plating for corner brackets and it works very well with the carriage bolts.
And yes, in my opinion stacking two extersions (80/20) and bolting them together is way stronger if you use steel plating.

I recently changed suppliers, and while the new bits and bobs are almost identical to the old ones, they go together more easily, and seem to be more rigid - which is nice :)