Quite an Unusual one

[Jonathan]

Brings back memories...



Anyway. How have you ensured alignment of the Z-rails - both their spacing (parallel to Y) and parallelism? I can't see any features for alignment, so either you milled reference edges in after assembly, spent time with a DTI and straight edge, or (I doubt) didn't do it? It almost looks like the spindle is just clamped by the plates with the arc-section cutout? If so I'd be a bit concerned about maintaining the accuracy of the rail alignment.

Then as we spoke it became clear that 1 ball nut assembly is ok, especially if fit with double ball nut.It also became clear that maybe i will not use at all the hammer but make separate machine.

I've probably mentioned this before, but I'm not convinced that a double not would actually work better than 1 nut here. In a double nut system the nuts are preloaded against each other, so a force is applied the load on one nut decreases whilst the force on the other nut increases. For any force above the preload force, all the force will be transferred to one nut.

Either way, as you implied, in general it's more economical to use a larger ballscrew (or larger rails) than multiples *unless* the spacing of the linear bearings is such that racking is an issue. I mentioned it here regarding rails and stiffness, but similar reasoning applies to ballscrews.

[Boyan Silyavski]

Brings back memories...

that creation of yours is exactly what inspired me for my Z

Anyway. How have you ensured alignment of the Z-rails - both their spacing (parallel to Y) and parallelism? I can't see any features for alignment, so either you milled reference edges in after assembly, spent time with a DTI and straight edge, or (I doubt) didn't do it? It almost looks like the spindle is just clamped by the plates with the arc-section cutout? If so I'd be a bit concerned about maintaining the accuracy of the rail alignment.

First of all all steel there was laser cut and holes laser drilled, which helped a lot /0.01-0.03mm accuracy of all cut pieces/. Then the aluminum pieces were machined <0.01mm

So knowing that the aluminum pieces were precise, i mounted first the rails on the separate side pieces, checking them to be tight corner fit against another piece of aluminum and straight edge. Later i mounted the 3 sides of the box using , straight edge, precise squares and digital caliper. So now i knew they were parallel to each other in all planes, /same distance/. Then i checked if the spindle enters and it was tight fit just easy enough to slide.

That told me till here everything is perfect/ cause the spindle was machined before 99.8mm OD. We were at the point of machining it and checked it against DTI and it seemed it was not necessary. That is the "good" original spindle with the 4 bearings.

Then knowing that the spindle box is mounted together under 0.01mm i just screwed to the side bearing blocks the side steel plates checking them flat and square against flat surface. Then i used some small clamps to not let them move back and forth.

So as all was mounted together maintaining that precision i laid it down carefully on top of the back Z plate. Now as you can guess the Z plate was not perfectly flat. So i spot welded the side plates/together with the aluminum assembly/ to the Z plate, but only at one side that so the previous assembly is square left right. See pictures above. I used also some clamps not to let it twist left right. Then i force clamped all down to the steel back Z plate , so now it was square and flat / cause the steel side plates wer cut by laser 0.01mm , remember? and i have mounted them perfectly flat against flat plate/ .


So now all was 0.01mm mounted together. I just carefully soldered spot by spot, careful not to heat the bearing blocks.


Later i took out all the aluminum assembly together with the bearing blocks and painted the steel assembly , masking the sides where the bearing blocks were meant to enter later So at certain places there is no paint, to ensure tight fit and not spoil the accuracy.

Same must be done for the back at the place where the ball screw nut housing on the gantry will be fixed to the back Z plate. I just left 1mm space in the drawing, to be shimmed, but due to 1mm less epoxy height, it was tight fit.

What i would say that a sincere judging helps here, one should not lie to himself and want to speed things, cause these are the moments where accuracy may be lost and accumulated.

So I fit the steel Z assembly to the gantry and squared it using the vertical Z bearing block surfaces to a straight edge across the long rails. Then i resquared the gantry ball screw, loosening it, going one end, tighten, going another end tighten and repeat. This to have the Exact same travel as the rails

So when i fit the aluminum assembly i had only to square it front back/ again using the long straight edge across long rails. See photo above. Then tightened the bearing blocks to the . That simple.

Something should be clear though. everything was designed to fit together using only 2 precision squares and 1m and 2m straight edges. No dial indicator was necessary at any moment. Everything was judged by the tight fit of the squares to surfaces and straight edges. I did so with the first machine i build and achieved 0.01mm precision.

So basically i will not use DTI until the moment i have the machine running. from experience it seems i can notice with naked eyes 0.05mm gaps without problem against the straight edge/ the epoxy story/ so i am happy that everything is tight fit.

When all ready i will check with dti and straight edge and report. But for now it seems i maintain the same precision as the first build and on that size of machine, well ... i am happy

[JAZZCNC]

So basically i will not use DTI until the moment i have the machine running. from experience it seems i can notice with naked eyes 0.05mm gaps without problem against the straight edge/ the epoxy story/ so i am happy that everything is tight fit.

Now now Boyan.!!! . . You contradict your self about lieing to one's self here with this statement.!! . . . . Your fooling your self if you think you can see "Five one hundreth's Gaps" with naked eye over the length or width of this machine.

Not saying your machine isn't or won't be accurate because I know it will or you will make it so. But I must say think your going to be surprised when time comes to cutting just how far out of Tram that spindle will be if you don't put a DTI on it. I also think it will be Bitch to setup looking at the pics.!!

[Boyan Silyavski]

What i meant was i can spot the 0.05-0,1 mm gap between a straight edge and something, say rail or other flat surface. Not that i can spot if the machine is straight or not over all its length or width. I spent a week just making sure the long rails are mounted straight and flat, not counting the epoxy.



Yeah, without DTI its difficult to say more.


What do you mean to tram the spindle? Its trammed already using 2m straight edge and squares. There will be no more tramming until the moment i cut some square aluminum shapes and first i make sure the gantry is squared by the limit switches and later do some stuff and see if there is something off judging by the final dimensions of the work.

Then the bed would be surfaced or head trammed first, but only if i am off by a great deal, depends on what results tell me. It is very easy in fact to tram it all as i always followed your advice of adjust ability making all through holes bigger.

Now about the DTI. I could clamp it now on one side rail and move the head assembly up down and see what DTI says but ... ok i went and clamped it. It says nothing, i mean i mounted all very well only using the squares and edge. Unbelievable but true.

I will power the whole thing then check and readjust if necessary, cause its very difficult to move all by hand. long distances i mean and i get bored.

At the end even if vertically is off with 0.1mm on 200mm travel/ which is not the case/, this is nothing. on 20mm aluminum sheet the inclination would be 200/20=10, so 0.01/10=0.01mm

[JAZZCNC]

You will tell instantly if the spindle is trammed correctly or not when you surface material with a wide cutter. If off then you'll get steps and it doesn't take much error to get steps. The pictures make it look difficult to get at bolts if shimming is needed etc.

[Boyan Silyavski]

Now comes one of the last parts. I frankly admit i was quite indecisive there, from the beginning of the design. So it was time to sit on my arse and make some calculations and think the things clearly.

The working area / table bed. May be it a theme for a whole new topic. i see many people are wondering how to do it differently than plywood, especially if they mean to cut aluminum and cool it.

Now lets be clear i am not talking about the machine bed structure nor the sacrificial board. I am talking about the working bed/fixing area and method which is in between the frame and the sacrificial board and which is water/coolant resistant and is strong enough for moderate aluminum milling

So lets see the options. prices are Spanish, but may be more or less the relations will keep in different countries. Some thickness prices are not known but can be extrapolated. 1kg of steel is ~1 euro, 1kg of aluminum 6082 is ~5euro,

-phenolic 10mm thick 65euro/m2 so as i see it needs to be minimum 20mm best 30mm thick ...
-marine ply wood 15mm thick ~36-50 euro per m2 , i see it needs to be at least 30mm thick.. so its good for a spoil board but expensive for top
-marine ply wood with phenolic top for truck flooring, now this is a good one, but its even more expensive and the phenolic will be very thin to surface

Now instead of writing here i have made some drawing with data for the better options:












I have spent all morning in calculation and last days rethinking the things. So for me its clear:

My choice will be UPN140. I have the bed clearance for it. It is cheap and very strong for the money. Like the last photo, 2 welded together, with T channel and DIY Tee nuts as per drawing. So i will drill a lot of holes and use them for fixture and big sheets will be fixed with clamps that will pass trough the channels. It will be screwed to the table with nuts that pass between the connection of 2 of the UPN. I will have to find a resistance welder from somewhere for clean job.



Note: Moment of inertia is x axis cause its in C position when measures are given, so a bit misleading. Anyway, its in the good for us direction.

last thing that i have not clear is if i will machine it both sides and machine the bed bellow, so all is flat when mounted and dismounted if needed. I am seriously starting to think to somehow mount a grinder on the Z or surface all using small bit, slow speed and coolant. i said before no steel work with that machine, but its quite tempting. And from what i have seen people have done it with much weaker designs.

One thing i know is that on top of that UPN140 i will use then thin phenolic sheet or even better scrap pieces, for sacrificial board. At leats on some part of the machine. On other i will use cheap expanded PVC sheet.

I hope that these calculations money/material/ strength will help people to evaluate properly what exactly bed they need.

Notes
-UPN profile can be cast filled with cement which will make things even better. Non crack cement for table tops and garage floors is enough for that.
-aluminum T channels are damn expensive so i did not even consider them. Even steel channels are very expensive, crazy.


PS2.
One question . For the the threaded holes to be closed to keep them clean , what is the name of the screw that is like a grub screw but is for flat screw driver?

[toomast]

PS2.
One question . For the the threaded holes to be closed to keep them clean , what is the name of the screw that is like a grub screw but is for flat screw driver?

I believe it is called SLOTTED GRUB SCREW.