Thread: RHS frame?

Just about every machine I have seen welded suffers from warpage and unless you compensate for this in your design you will have problems. This means having the area where the X axis rails mount machined flat after welding and shimming or using adjustable fixings on the bed of the table.

The first step to a good machine is to make the base. All too often a machine is made on a bench and then later moved onto a stand - guilty of that myself. I think the best approach is to make the stand first and this can be welded. This then gives you a rigid structure and hopefully plenty of mass to build the machine on. Mass in the base is important as the inertia produced while running the machine can be considerable. Of cousre you need to attach your machine to the stand to get the benefit.

The machine frame I usually build from flat steel for the sides (channel is a good choice also) and angle everywhere else and I use MDF jigs, straight edges and lots of clamps to position all the joining members. I drill and tap all the connections. For the gantry I would recommend aluminum as it is lighter, straighter and dimensionally more accurate than steel. 80/20 or Item profiles are perfect for a gantry beam.

I know I haven't answered what you asked but I am offering an alternative.
Perhaps some of the fellows that have welded their machines together can give their experiences to balance this out.

Good choices on your other components.

1100 X 900 is a large unit to weld.
Only option if you go down this path is to have the unit surfaced to ensure it is flat on top.

I know a bloke who has done this on a moving table, but the unit was half the size and easier to surface finish.

/M

Depends what your aiming for and the precision you require.

I built a machine called sloppy its a welded frame not by me but by a welder 1200x900x240 cutting area I called it sloppy because all that I built it for was panel cutting/cut through work not precision work I was happy with a tolerance of 1mm I ended up with better then that the gantry sides are MDF lol I will replace them one day but its doing close on 15hrs a week and is still as good as day one so I wont fix what isn't broken + I cant afford the downtime.

You really need two things an experienced welder that understands steel and a good steal supplier that can guarantee straight steel I was also lucky that they cut to the exact mm as well and I don't pay any more for it, its good when your in a small town they fight for work and really look after you.

Duel screws on the X I would like to find out why this is required I see it a lot on DIY machines these days but it seems like a lot of work I understand if your using R&P its required but I am driving it using 1 1605 from chai easily at 6m a min screw length is 1200mm with a 269oz stepper all works fine for me and my gantry is heavy I could go to 9m but really need to do some more bracing on the legs first one day I will finsih what the welder told me to do .

So can it be done well yes it can depends on what you want the machine for you may need to shim the table a bit but it is possible.

If I was to build another and didn't have my mate across the road I would go down Rods path with a single screw underneath direct drive its simple drive and it works.

Anyway just my thoughts.

Willy

I built the bed of my machine entirely from RHS, but it's all bolted together. No welding due to the warpage factor. It works pretty well, but does need to be mounted on a pretty solid base otherwise it will twist a small amount.

https://www.woodworkforums.com/attach...ssembled12.jpg

As Rod suggested, I built the gantry from aluminium.

The dimensions of my build are similar to what you want and I also am using the Kress FME800 spindle which is a very good unit.

My build is here if you want to have a look: https://www.woodworkforums.com/f170/new-cnc-build-82186/

Cheers

I built my 2nd machine from 75x75 and 125x75 RHS and SHS but because it was my first serious time welding it warped like anything + the steel is not as perfect as you would think on its own, then add welding it will always be out.

Hi,
I am part way through my first build and I have used welded 50 x 50 SHS for the frame. Welding will always cause some deformation and this means the fabricator must allow for this in the setup stage of fabrication. All of this assumes you have experience with welding and fabrication, if not then I would follow Rod's suggestion.

My machine also has an RHS gantry which is 150 x 50 x 3 mm with 12 mm plate welded to either end. Weight wise the 150 x 50 x 3 is 6kg per metre. This is drilled and tapped to take the gantry sides and yes it requires either machining or hand fitting to true and square the gantry sides but this is not a problem if you are handy with a file and have large squares and straight edges etc and of course time.

My build will have 16 mm aluminium plate as the table and the rails for the X axsis will be mounted on the plate which makes truing a little easier.

Good luck with the build which ever path you take.

Cheers
Steve

Steve,
I learn new tricks all the time here - that's pretty clever attaching the rails to the table.

Thanks Rod,
I just thought it may save me some work in truing every thing. Of course I still need to check the table to Y Axsis but it should be quicker.


Cheers
Steve

Thanks to all those who gave advice on my planned RHS build. I had the good fortune to come across a quantity of aluminium profile in an online auction, so have decided to build the bed of the CNC router from aluminium and attach it to an RHS base. I'll start a new thread on this build very soon, now that I have most of the materials and a much better idea of how to tackle the project.
Cheers