All steel, no welding, 2000x1300x250mm

[eurikain]

Thanks for the replies ! It's nice to see the support !

You are right, welding the rails will cause bending. What about brazing ?

Pass the next paragraph if you're not interested in my totally subjective opinion and prefer getting to the more relevant part of my post :D

Now, here is the problem I have with the fully supported rails: I have looked into that option for quite a while, but nobody at AliExpress will accept to ship 2000mm round supported rails to me... I asked already, they shipped the SFU2010 2000mm lengths without any problem, but won't take the risk of sending those rails over 1500mm. Now that's only one side of the problem... the other one is that shipping cost is just a waste of money... there is no real added value to those rails except the fact that they're round stainless steel rails mounted on stainless steel supports. Now this is just my opinion, and I know that using them would be the best option, but I just feel really bad spending $300 on shipping on a $100 rail, that's just not enough cost effective for me and not in the philosophy of this machine :(

Even if you insisted on not using the supports that the rails comes with, you can unbolt them and use the pre-drilled/tapped holes in the rail to attach your own supports...

Now that's a winner :) But, I can get those wholes drilled and tapped in a 20mm stainless steel shaft, here in Belgium, with $0 shipping cost. I could include that into my design as well ! Do you have a picture of a supported round rail where shaft and support are separated ?

[Wal]

Do you have a picture of a supported round rail where shaft and support are separated ?

I don't, I'm afraid, but here's a link to some data etc. for my TBRs:

http://www.zappautomation.co.uk/mech...aund-rail.html

IIRC even though the holes were spaced equally, there was no control over how far the first/last bolts fell from the ends of the rail - it didn't matter as I didn't need to separate the shaft from its support and I had full control over where I was putting my own mounting holes in the supporting base. I imagine it matters a bit more for you, but you could always buy over-length and then cut down so that the holes fall where you need 'em to...

>As for the rails...somehow I have a feeling that you will end up with HIWIN stuff.

Yes yes! (...and I like my round rails, but profile is the way to go..!)

Wal.

[routercnc]

On the rail lengths problem I know you can butt individual profile rails together to make longer rails but not seen it done on supported rails. I wonder if you cut off a piece of the supporting extrusion you get with supported rails (say 200mm) and use it to bolt 2 shorter rails together ie a joining piece. Because the support is continuous and has a shallow radius on the top which the round rails sits in it should help align the rails to each other. You could then order 2x 1m rails . Not tried it but something to think about.

[Boyan Silyavski]

Dont forget to leave space for adjustments. Even if precisely laser cut, sheets bend, etc.

I would say oversize all holes by 2mm diameter

[eurikain]

Something fresh and new!

Thanks ! I apreciate the compliment :D !

Your calculated weight numbers seems to be very low! 10mm and 15mm steel is heavy stuff...

I know, I have the same feeling, but I made sure that all parts were assigned non allied steel... so.. I don't really know what to think :/ Only the shafts are set to allied stainless steel.

But good rubber hammer will get it fixed :D

What do you mean ? I know what a rubber hammer is (at least I believe so ^^), but do you think that'll be enough to straighten it ?

You have to somehow make the openings for M10 nut pressfitted otherwise the nuts will fall out. That especially when you assemble the gantry...

Actually, the spacing between the nut and the part is .1mm on each side. The reason for that is that I want to compensate cutting accuracy, plus tolerance for bolts (I've checked a sample and they're not always the exact same diameter, weirdly).

or you have another solution for it?

I do ! Good old tape ! That will hold the nut while inserting the bolt :)

Please dont go with the round rails !
it will ruin what is looking like a nice design
thats all i have to say :S

I hear you :) Look at the end of this post for an answer ;)

I don't, I'm afraid, but here's a link to some data etc. for my TBRs:
http://www.zappautomation.co.uk/mech...aund-rail.html

Thanks a lot !

IIRC even though the holes were spaced equally, there was no control over how far the first/last bolts fell from the ends of the rail - it didn't matter as I didn't need to separate the shaft from its support and I had full control over where I was putting my own mounting holes in the supporting base. I imagine it matters a bit more for you, but you could always buy over-length and then cut down so that the holes fall where you need 'em to...

True, it does matter for me, but as you said, I can always buy over length and then re-cut to fit my needs.

On the rail lengths problem I know you can butt individual profile rails together to make longer rails but not seen it done on supported rails. I wonder if you cut off a piece of the supporting extrusion you get with supported rails (say 200mm) and use it to bolt 2 shorter rails together ie a joining piece. Because the support is continuous and has a shallow radius on the top which the round rails sits in it should help align the rails to each other. You could then order 2x 1m rails . Not tried it but something to think about.

That sounds like a good idea. I'll think about it, but I am worried about the moment my SBR blocks will roll on that junction... that might cause a cut "hick up", couldn't it ?

Okay, allow me to state it again:
Using unsupported shaft in this machine will be a waste of money and effort!
Building this thing in steel allows it to be a good performer, using unsupported shafts will allow flex, making the results no better then the same thing built of plywood.

Who said shafts were unsupported ? They're supported every 220mm. Go ahead and try to bind/bend a 220mm long 20mm thick plain stainless steel shaft. Yeah, probably with a 200kg Z axis, still... As currently designed, the Z will probably not exceed 15kg. Add cutting forces, let's say you go up to 40kgs (and I'm being generous ^^), considering the Z is supported in 4 points on 2 shafts, I honestly don't think binding will be an issue. But go to the end of this post for a proper answer on that :)

Then two general remarks on the design:
1: It seems to me that you will not be able to assemble this thing, as the nuts will be falling out all the time.

The solution is to assembly it smartly. Actually, two solutions exist: 1. use tape to hold the nuts in place while inserting the bolts. 2. assemble parts in an order that will allow nuts to fall on the ground instead of inside a closed space.

2: If you add tabs+rectangular holes here and there to position parts, you can probably glue the thing together, if you choose the right kind of epoxy.
If not using epoxy you can still use an occasional spot weld to fix a tab in its hole.

I like that advice very much :) I see this as a big Mechano (if you guys know that toy brand). What kind of epoxy are you thinking about ?

Dont forget to leave space for adjustments. Even if precisely laser cut, sheets bend, etc.
I would say oversize all holes by 2mm diameter

Good idea if laser/plasma cutting. Water jet cutting might be a solution.

General answer for the four main concerns:

1. Shafts aren't the way to go, they're bad, bad, extremely bad, up to the point that you'd be willing to whip me if I use them :D

People, I hear you ! But plear hear me too :) I know most of you like the HWIN rails / blocks, and I know for a fact that they are far better than SBR/TBR blocks with round rails. However, my original idea was to integrate the supports in the design, and I don't want to change it. BUT, I am going to compromise with you all: I will keep the integrated shaft supports, go with shafts and SBR blocks (I have already bought them a month ago, plus I'm interested to see how it turns out). HOWEVER, I will add to the model holes for HWIN rails and blocks. IF shafts turn out to be a bad decision or if I'm just not happy with the result, I will cut off the supports, buy the HWIN rails / blocks and just mount them on like nothing happened. I think that will make you all happy ! This is not a waste of money since I've already bought the SBR blocks, and shafts will be and additional cost of $50. This way, I git it a shot, and if it works, it's a $600 minimum savings for me. Otherwise, it's a $0 loss as I will happily sell those blocks to someone here on the forum, and if no one wants them I will keep them for whichever exotic project I decide to work on :)

Now, considering this, can anyone tell me what size HWIN rails/blocks I would need for this machine, so I can get a quote from my favorite AliExpress seller Kevin Ho ?

2. Nuts will fall when assembling.

Tape will hold them from falling.

3. Welding shafts on the supports will make them bind.

Sure, I trust your experience. I will ask the welder shop to make a test with two fake supports and one short shaft. We will then measure the binding. However, I think that you're worrying too much on this. Binding will happen if the shaft gets too hot, which can be avoided by doing very short runs (few seconds long). If all else fails, I will get the shafts and parts drilled and tapped by a profesionnal turner and let him mount them. And if that doesn't work, I'll go with option 2 proposed in point 1 (cut off supports and go with HWIN).

4. Plasma cutting and laser cutting will cause parts to move / bind / shrink, in other words change and cause misalignment.

Sure. I contacted the cutter on Friday and they said they're going to use a water jet cutter. I asked about accuracy and they said they can go up to .01mm accuracy. I also asked about cut straightness, because I've heard that water jet cutting looses accuracy on the bottom of the cut. For example, if you want to cut a 10x10mm square out of 10mm steel, the machine will cut 10.01mm x 10.01mm on top but 10.02 x 10.02 on the bottom. The cutter I called said that it is true but that effect can be overcome if you sonfigure the machine correctly. When cutting the parts, they (and I'll be there to check !) will do some test cuts until they have the right setup.

Alright, so here are my takes on what you guys have said in the past few days. Modeling is going great, gantry is almost done. I've had to stop modeling for two days because I traveled a bit :) Renders of the model will come soon :)

I am very thankful to all of you that are commenting the design and giving advice ! I surely will read you, and try to find the best (function and cost wise) solutions to the issues you raise.

Cheers from a warm sunny Belgium !