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  1. #321
    Most excellent machine build ,I enjoy very much the videos and I hope one day I will make good use of all thiaw tips you shared!

  2. #322
    Thanks Andy, Nick. I'm just a hobby machinist and just passing on what I have learnt along the way. Glad it was all helpful.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  3. The Following 2 Users Say Thank You to routercnc For This Useful Post:


  4. #323
    OK so yesterday I managed to take some measurements for the X and Y stiffness of the new Atlas Mk4 machine.

    The machine was positioned so the gantry was half way along the X axis, and the Y axis was positioned at the mid point of the gantry. So the X and Y positions represented worst case. The Z axis was lowered 50 mm from home in a typical machining position.

    I used a digital luggage scale with a hook on the end to pull on the spindle just slightly above the collet nut (6mm end mill was inserted), while a DTI was pointed to the round section on the collet nut just above the flats.

    5kg load was applied (~50 N) and the reading in for both X and Y was somewhere around 0.01 - 0.015 mm. I'm wondering how reliable this reading was given the needle barely moved and 0.01 to 0.015 makes quite a difference on the stiffness values. I guess I really need to buy a 0.001 mm DTI !

    Anyway, for Atlas mk4 this works out at:
    X between 3333 and 5000 N/mm (0.015 and 0.01 mm respectively)
    Y between 3333 and 5000 N/mm (0.015 and 0.01 mm respectively)

    My previous mk3 machine was:
    X 1000 N/mm
    Y 1250 N/mm

    So up to 5 times stiffer. It certainly sounds different when machining and as you might have seen in the videos you can certainly take a good cut so long as there is some lubrication. I didn't measure Z this time as it was a bit awkward Vs the previous machine.

    I did not have long to explore further but just before I finished I quickly pulled on the ballscrews when the DTI was still on the spindle and could make the needle move a bit. So maybe the limit is the stiffness of the small AC bearings in the ballscrew housings, or come to think of it they might be the deep groove ball bearings? Anyway I think as it is all working well I should stop there otherwise I will never use it to make something !
    Last edited by routercnc; 18-02-2019 at 08:18 PM.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  5. #324
    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 Click image for larger version. 

Name:	telescopic-cover-for-cnc-machines-500x500.jpg 
Views:	49 
Size:	25.2 KB 
ID:	25475

    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.

  6. #325
    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
    Last edited by Voicecoil; 19-03-2019 at 09:05 PM.

  7. #326
    Quote Originally Posted by paulus.v View Post
    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 Click image for larger version. 

Name:	telescopic-cover-for-cnc-machines-500x500.jpg 
Views:	49 
Size:	25.2 KB 
ID:	25475

    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 Iíve since added soft limits and it works well
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  8. #327
    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
    Last edited by routercnc; 19-03-2019 at 10:19 PM.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  9. #328
    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.
    Last edited by Voicecoil; 20-03-2019 at 04:50 PM.

  10. #329
    Lee Roberts's Avatar
    Lives in Wigan, United Kingdom. Current Activity: Viewing Moderator Control Panel Has been a member for 9-10 years. Has a total post count of 2,631. Received thanks 191 times, giving thanks to others 681 times. Made a monetary donation to the upkeep of the community. Referred 9 members to the community.
    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.
    Last edited by Lee Roberts; 3 Weeks Ago at 07:20 PM.
    .Me

  11. #330
    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 . . .
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

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