Joe's 1000x600x200 steel and aluminium router started

[devmonkey]

So I just did some maths, if 've got all my units correct, a 100N force on the cutter exerted at 300mm below the centroid of the gantry cross section and half way along the 1000mm Y axis would cause a deflection at the tool of approximately:

160x80x16mm channel is 39cm^4 - deflection 0.22mm
160x80 ITEM heavy profile 390cm^4 - deflection 0.022mm
160x80x16mm box is 1400cm^4 - deflection 0.006mm

I guess that 100N is unrealistic and would break the cutter first.

I'm going to have to drill all the holes anyway, is the bog standard 6" x 3" x 3/8" aluminium extruded box section flat and twist free with parallel sides?

I was looking at the Item profile extrusion since I thought it would give me parallel flat sides without having to process it. My mill table is only 700mm long, not quite enough to surface the entire gantry without re-locating the work which is difficult to do accurately in plane.

I'm also sure I've seem some pictures on here of peoples gantries constructed from plate?

[JAZZCNC]

I'm also sure I've seem some pictures on here of peoples gantries constructed from plate?

Yes probably seen gantry I've shown built from plate and few others used it or adapted to there machines. It makes for a very stiff gantry,

However, it needs a lot more work compared to HD profile. I've used all methods of constructing gantry's and HD profile is by far simpler with more than enough strength for any Router cutting materials up to Aluminium.

Aluminium Rect section doesn't compare to HD profile in terms of resonance and vibration dampening and this is should be more of a concern than twisting deflection you seem to be chasing if you want a good Router.
There is no cutter you will use that will withstand forces enough to twist a gantry made form any of these materials before it snaps. However, Resonance will affect any cutter and the smaller the cutter the worse it gets. My advice is to Stop chasing twisting etc and look more to lowering resonance if you want a good Router.

[Voicecoil]

Aluminium Rect section doesn't compare to HD profile in terms of resonance and vibration dampening and this is should be more of a concern than twisting deflection you seem to be chasing if you want a good Router.

That's an interesting point and worthy of investigation. I've saved the impulse response files from a length of the 6 x 3 x 3/8 box, does anyone have a short-ish (~600mm) length of 160 x 80 profile they can lend me to do a comparative measurement?

[devmonkey]

Yes probably seen gantry I've shown built from plate and few others used it or adapted to there machines. It makes for a very stiff gantry,

However, it needs a lot more work compared to HD profile. I've used all methods of constructing gantry's and HD profile is by far simpler with more than enough strength for any Router cutting materials up to Aluminium.

Hi Jazz,

Thanks for the advice. Do you have any pictures or wise words on how a 'stiff' gantry was made with plate? From the calculations I did a simple channel from 16mm plate is not sufficiently stiff in torsion at 1/10th that of 160x80 profile.

I'm trying to reuse a set of HGR15 rails left over from another project on the Y. These were originally purchased to replace rails on a much larger machine that had rusted badly, since then that machine has been written off.

15mm rails are too narrow to go over an 8mm slot, this means they will need to be drilled and tapped into the centre flat section between two slots or another plate milled to bridge the slots and then mounted to that. If the latter then it isn't much more work to mill up a front plate as well.

If I already had 20mm rails for Y then the profile would be a no brainer as the rails could be bolted straight into the slot.

[devmonkey]

Right I've made a decision!

I called around a load of my usual aluminium guys, Smiths, Aalco, Blackburns, plus a couple of local metal shops. No one has any 6x3x3/8 box on the shelf (even Aalco who have a warehouse near me about 10 acres in size) and although they could get it I would need to buy a full length. To be fair I didn't try Simmal.

I've built two previous machines using 6x2x1/4 box and they worked fine albeit I had to shim the rails, only very slightly as I didn't have a mill back then and I had to bolt blocks into the ends to bolt into (not required on the 3/8 box). Anyway I'm just going to go with the original plan from the first post in this thread, will order some 160x80 Item heavy clone from KJN tomorrow.

I will first try to just mount rails directly to the central flat on the profile, if this turns out too wobbly I will plate over the slots and fix rails to plate.

[devmonkey]

I've started milling parts for the Z.

Front plate and rail spacers finished, all fits well. These large plates take an age to mill out on my manual mill.



At least drilling the holes accurately is simple with the DRO.


Also took a delivery of bolts for the machine:

[devmonkey]

Finished the Z back plate so have now assembled the Z. Everything fits perfectly. All 4 long edges of the large front and back plates were milled in a single fixture so these will all be reference edges for aligning the rails and also tramming the Z on the gantry.



Pockets for the ballscrew mounts, these weren't perfect were supposed to be 1mm deep, infact 1.28mm so will need a thin shim between front plate and ball nut holder. TBH ballnut holder is not a precision item, rather it is a cast lump, so probably would have needed shimming anyway.






I'm now waiting on the extrusion to arrive for the gantry as I need this to measure off for the Y bearing plates, gantry end plates, etc. Hopefully should be here early next week.