Here we go again . . . MK4

[paulus.v]

Thanks a lot for the stiffness measurements!

I had to put aside the research and design for my new cnc, that's why I didn't bother you.

If you accept challenges, here is one for you, as I see you are an expert at sheet metal bending: dust covers

Re homing/limits, I have set in Mach3 the sensors for both home and limits as well as setting soft limits with the min. max. travel. It works nice, stops before "hitting" the sensors in jog mode and I get limit warnings when g-code is out of the machine travel. With this setup I have never hit the hard limit switches so far.

[Voicecoil]

Hi Routercnc I've just been going back through one or two of your videos when the dire internet here allows, and I'm curious about one of the things shown in episode 23, where you square up the gantry.It looks like you're achieving this by having independent limit/homing switches on each of the horizontal axis ballscrews, but doesn't this leave the whole assembly under quite a bit of tension?? or do you home it with the screws slackened off a tad then tighten?And does it mean you need to have separate drives from the control software for each of the steppers?
Although it's not assembled yet I'm trying to figure out how I will square up the gantry on my little machine, bearing in mind that my gantry is quite short (~600mm) and a very rigid bit of box section.
Thanks, Trevor

[routercnc]

Hi Trevor
Yes you can only use this to square up a mm or so otherwise there is too much tension. You need to make and assemble it as square as possible first. Depending on the design you might be able to slacken the gantry bolts and square it up using separate home switches then retighten as you suggest.

I had to be careful with mine as to do independent homing I needed to switch off slaved axes temporarily. This meant my Z motors were also no longer slaved (I have 2 on Z) so after homing X I switched slave back on and now usually just home off the left sensor with the motors slaved. I check each side with callipers to ensure they are still the same distance from the end plates.

Yes separate drives are required plus a spare axis on your break out board (usually A). You can’t do this trick from a single motor with belt coupling to the other ballscrew and would need a way of making tiny adjustments on one ballscrew relative to the other mechanically. Probably the grub screws holding the pulley onto one of the shafts

[Voicecoil]

Thanks very much for the clarification. I'm not so worried about squaring the gantry on the horizontal sense (having it parallel to the bed) - I have a big digital height gauge so can get that initially set pretty good, besides mine's single motor on the Z.- It was more the X,Y squareness for which the only "old fashioned" tool would seem to be a fairly huge and vastly heavy 3 way angle plate. I'm running twin motors/screws on the long axis (which I call Y since I look at it from the front), but was going to simply parallel up the inputs to the drivers, in the light of this maybe I need to have a bigger BOB or a bit of switching.

[Lee Roberts]

Would a 3.1Nm motor really find it that much of a challenge to drive 4 ball nuts all engaged at the same time on your Y ?

Super cool of you to do what your about to do btw

P.S Don't forget we have an open source section/forum.

[routercnc]

I'm not sure if I'm honest. To drive 4 ballnuts without pre-load would be fine I think, but when the ballnuts are clamped together there is an extra load to overcome, and the Y/Z is pretty heavy. Is it worth the risk to have missed steps on a critical job? Not sure.
Decided to leave it like that and put some pre-load between the front and back ballscrews instead.

Sending pm shortly . . .

[routercnc]

Hi Lee, pm sent . . .

[routercnc]

Thanks a lot for the stiffness measurements!

I had to put aside the research and design for my new cnc, that's why I didn't bother you.

If you accept challenges, here is one for you, as I see you are an expert at sheet metal bending: dust covers

Re homing/limits, I have set in Mach3 the sensors for both home and limits as well as setting soft limits with the min. max. travel. It works nice, stops before "hitting" the sensors in jog mode and I get limit warnings when g-code is out of the machine travel. With this setup I have never hit the hard limit switches so far.

That sheet metal looks like a challenge. I guess they are concertina type? I think Chris Deprico (?) on YouTube made some and it looked very fiddly making the X bracing supports underneath which guide it.

Yes I’ve since added soft limits and it works well