CNC Router V1.0 (For Cutting Multiple Materials)

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Originally Posted by biketrialsdave

Hmm maybe it's time for yet another re-think then...

I don't want to go OTT with the design but obviously it needs to be useful. What are you opinions on the gantry design as it stands so far? Are there any other alternatives to a steel box section base?

Thanks for all the help,

Dave

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Dave don't get me wrong I'm not saying profile won't work because it works great and I use it all the time but it does need to be supported and braced correctly and by this I mean not using in the normal manner profile is used IE: using corner brackets etc. I'm also not saying your design is flimsy or weak just not has strong as you may be thinking. It will certainly have some chatter in harder materials as the frame vibrates.
For this high side design to work best with profile, esp when on it's thin edge you need to brace the hell out of it using plates.

Your gantry is ok-ish but I would have a bit more strength in the bottom profile as this takes the most the cutting forces. To be honest I'd have the L shape layout of the profile at the bottom but with lower profile laid flat.

I understand your reluctance to weld but it really isn't difficult or needs to be expensive. Don't need a Mig and like as been said cheap stick will work fine.
If you don't want to weld then how about finding someone who can weld and have them do it for you.? If you cut and preped all the steel it wouldn't take someone long to weld that simple frame.! . . 2 hours Max and I'm allowing for a very very slow welder there.!! If all steel was cut and preped it would literially take me 30-40mins tops just for the welding.

Hmm well I do have an arc welder somewhere in the shed. Not touched it for years and was never any good at it! May need to get practicing...

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Originally Posted by biketrialsdave

Hmm well I do have an arc welder somewhere in the shed. Not touched it for years and was never any good at it! May need to get practicing...

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Get it out and get practicing. Don't use old rods and buy good quality rods not some cheap rubbish from car boot as they make all the difference. Keep them dry and stick in oven on low heat for 15 minutes before starting. Welding new metal like Box section is a piece of piss with a stick welder. Also Just realise you don't need Xray quality welds and Just like Snow makes every body's gardens look the same so does a good grinder and paint on pigeon shit welds. . .:encouragement:

Just pulled it out the garage, its the one in the link below. Very cheap and cheerful. Only a 100A output.. What sort of thickness steel box section would be best to use? 3/4mm?

http://www.metals4u.co.uk/welding/we...sp?prd_id=3124

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Originally Posted by biketrialsdave

Just pulled it out the garage, its the one in the link below. Very cheap and cheerful. Only a 100A output.. What sort of thickness steel box section would be best to use? 3/4mm?

http://www.metals4u.co.uk/welding/we...sp?prd_id=3124

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4mm will be better than 3mm but either will work. With 100A you'll be limited to 2.5mm rods which will be better suited to 3mm.

I will find all my gear and get hold of some scrap metal sometime this week! :) It's always good when you find a reason to use an untouched tool! Out of interest, how are people bolting their linear rails to box section? Bolt all the way through both sides?

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Originally Posted by biketrialsdave

I will find all my gear and get hold of some scrap metal sometime this week! :) It's always good when you find a reason to use an untouched tool! Out of interest, how are people bolting their linear rails to box section? Bolt all the way through both sides?

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You can't bolt all the way through as it would squash the box section without spacer tubes I used 5mm box section so just drilled and tapped it but others have glued a steel plate inside the box section with gorilla glue and then drilled and tapped. As Dean says you don't have to be super accurate because you can use epoxy on the top with a moat between the rails so that it levels out on the same plane.
When and if you come to this step just ask as quite a few people on here have used it. I used the Wests System which is ultra slow curing ie 15 -20 hours and so levels out very well ..Clive

Why is it not possible just to drill a bigger hole in the bottom face of the tube and nut up to the underside of the top face? G.

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Originally Posted by GEOFFREY

Why is it not possible just to drill a bigger hole in the bottom face of the tube and nut up to the underside of the top face? G.

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It is possible Geoffrey but to be honest it's not needed. Mostly I use 4 or 5mm without any problems but in the past I've fitted rails to 3mm box with no issues. The fine pitch gives enough threads engaged and because of the number of bolts you don't need to swing on them to tighten down.
I just use spring washers with loctite on threads and never have any trouble. The rails on my machine are into 3mm box and have been on for over 6yrs without any bolts coming loose so it works well enough.

When I started building my first frame I (stupidly) decided to bolt it together, I was worried but stripping threads etc so I did some experimenting...

The test piece was 4mm steel box section drilled and tapped for use with regular M6 socket screws. With a screwdriver and a hex head I couldn't do the bolts up tight enough to strip or damage the thread in the box section. With a regular Allen key I generally couldn't damage the thread, after repeated re-tightening as tight as I could do by hand I did manage to make a couple of the test holes a bit loose. With a cheater bar on the Allen key I could strip the threads and using a drill driver without torque limiting I could strip the threads. My conclusion was 4mm box + M6 was more than strong enough for what I was doing.

I also experimented with some 3mm box + M6 and concluded it wasn't good enough. You can get a thread in it but it's clearly not much good. M5 worked and M4 (which is what I suspect your rails will be using) was fine.