Thread: Linear rail question
All good feedback! Been thinking alot and got a good contact for z-plate milling, so thats coming along ;)
New thinking and new problems!
Im going with welded steel frame, around 60x60x3mm for x rails and legs.
Now for the question.
Can I use something like 40x40x2 or even 30mm for bracing?
What measure should I use for the bed? The total size should be 1500x1500mm (maybe smaller in y, total 1000mm but I would love the posibilities of 1200 workable area)
Im thinking of making a frame and then crosssections along y axis only about every 300mm? Maybe with 40x40x2mm steel?
And then one under all of then in the x axis in the middle for sag support?
Would love to show a cad drawing here but my computer died and Im restricted to using a phone at the moment.
Get your PC working and show Pic of what your meaning because without it not easy to visualise and could easily be talking at cross purposes.
Also at that size then I'd go with 5mm wall not 3mm. This will give enough material for drilling and tapping but more importantly help lower resonance from thicker wall. The difference 2mm makes is quite noticable on resonance.
Smaller tube size for bracing is fine provided there's enough of it and bracing in the right places. I'd go with 40x40x3
Hello again all you CNC-jedi!
Jazz, still have no computer at home, the frame question has to wait. But here is another!
Ive read that Ali extrusion isnt flat enough to mount rails to (but Ive seen many builders do so) What do you think about machining a flat steel strip maybe 30-40mm wide, 4-6mm think and mount this between the rails and extrusion? Just drill through and use a longer bolt for the rails? Or would I just get the same imperfektion in the steel when I thighten the bolts?
Has anyone use this chinese type of rails?http://m.aliexpress.com/item/32446258288.html
Autocorrect om a phone is a bitch when not using your own language ;)
There are a few things you need to take into account thou. Rail width and slot size need to be matched. For instance I wouldn't use 10mm slot with 15mm rails as this can cause problems due to profile slot having rounded edges. You need plenty of rail each side of the slot.
I use lots of profile with 8 & 10 slots but always with 20mm rails and don't have any problems.
Aah that sounds much better! As I mentioned earlier I will route mostly hardwood. Oak for the most part!
I will go the "standard" way with raised x-rails from the steel frame. Epoxy leveled. Then use a 160x80 Ali profile with 8mm slots for the gantry.
Im going to have the gantrysides watercut from 10mm steel, or is it better with 20mm Ali?
The Z plate will be 20mm Ali but Im thinking about using 10mm steel for the y-car sounds good?
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I'm finally CADing my design. Quick question to all you experienced ppl, how high should you raise your x-rails?
I'm thinking about using 20mm sacrificial bed and want maybe 60mm workable Z depth when finished.
Can't see me doing any job higher than that.
So 20mm bed, 60mm work, 50mm tool? And then the collet and lower gantry bearings and plate add another 70mm?
Really you want to keep the x axis (gantry assembly?) as close to the bed as you can.
I can't remember what I went with on mine but I think I left around 150mm clearance from the lowest part to the bed, this will be reduced though because like you I'll have a bed plate, sacrificial plate and so on.
My machine was originally aimed at sheet work, in wood, so that's what I had in mind at the time, though I didn't know as much then as I do now and a few things changed along the way.
So again keep it as low as you can but do consider if at some point you may want to add an additional rotary 4th axis to the bed, the size of a chuck for instance would need to be accounted for, you may just need to lay a chuck on the bed as a clamp or for use in an indexing operation.
Last edited by Lee Roberts; 19-07-2016 at 01:39 PM..Me
Your thinking correctly but do your calcs with the longest drill your likely to use rather than cutting tool. Also remember Clamping etc because you'll need to retract above it.
Last edited by JAZZCNC; 19-07-2016 at 01:44 PM.
I wouldn't DIY a cnc with less than 100mm real Z travel to sacrificial layer. Or even better - no less than 150mm Z travel to bed with tool mounted. That means by moving the spindle up and down an additional height could be gained, so no less than 180-200mm from lowest gantry or Z part when Z is raised to table bed/ the clearance/.
Doesn't matter if would work with flat sheets or not. Additional sacrificial layers, vices, fixtures, holders, clamps, part height... that easily eats from your travel. I have a small machine with 100mm travel, have made with 200mm and now my big one is with 300mm clearance. But that's my design point of view of course. So to resume- 150mm Z travel and 200mm clearance will be a big ++++++++++
I love this forum! ;)
When doing my math I got to 200mm raised x-rails. Quickly realised that lower y bearings add the same hight as the x bearings so they should be removed from the equation.
Will do a cad over the next few days and post it here.. hopefully you have some input
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