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  1. #11
    Based on your recommendations, I ordered the rails and carriages from Fred at BST - excellent communication, great pricing and quick turnaround. Time from payment to delivery was 8 days (paid Sunday evening, received Tuesday the following week).

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    I'm going to test bolt things together this weekend to measure up various bits and pieces and see how she slides. I'm going to get someone local to machine a few bits of aluminium for the extra bracing on the gantry. Do you guys lubricate the carriages before putting them into operation? They feel like they're a little 'dry' out of the box, but not sure if that's the ZA preload I'm feeling?

    Now it's down to selecting the ballscrew for the X axis. Some folks on a Dutch forum suggested going for dual ball screw to prevent the gantry from racking. Gantry width is 800mm, and as mentioned I plan to mount a 2.2kw Teknomotor spindle. This machine was originally designed with steppers in mind. Will adding servos (with their potential for greater acceleration/rapids) make a duals screw with individual drive a more stable solution? If so, 2020 or 2010 for both, or downsize to 16mm screws?

    Also, is there any significant upside to getting a C5 ground ballscrew (e.g. a TBI from Tuli) vs a C7 screw from Fred here?

  2. #12
    Quote Originally Posted by Mattia View Post
    Do you guys lubricate the carriages before putting them into operation? They feel like they're a little 'dry' out of the box, but not sure if that's the ZA preload I'm feeling?
    Grease them when your ready to use the machine, there is enough grease inside them for setup etc but not enough for running.
    The stiff and notchy feel is quite normal, when greased and in use under weight they run smooth.

    N
    Quote Originally Posted by Mattia View Post
    ow it's down to selecting the ballscrew for the X axis. Some folks on a Dutch forum suggested going for dual ball screw to prevent the gantry from racking. Gantry width is 800mm, and as mentioned I plan to mount a 2.2kw Teknomotor spindle. This machine was originally designed with steppers in mind. Will adding servos (with their potential for greater acceleration/rapids) make a duals screw with individual drive a more stable solution? If so, 2020 or 2010 for both, or downsize to 16mm screws?

    Also, is there any significant upside to getting a C5 ground ballscrew (e.g. a TBI from Tuli) vs a C7 screw from Fred here?
    At 800mm your at the limit of a single screw and personally I would use twin screws, esp if using servos.
    Regards the screw size then it depends on the length, if over 1100mm then I would use 2020 with a 2:1 ratio, again even more so if using servos because of the higher RPM's servos run at. The ratio will half the screw speed but bring the resolution and federate back inline with 10mm pitch.
    If between 1000-1200mm You could use 1616 and do the same but the difference in cost isn't worth taking the trouble, and if over 1200mm then 20mm is the best choice.

    Just getting C5 rolled screws over C7 is worth it and ground goes a step higher but so does the cost. End of the day it's down to how a good a machine you want and your budget. BUT.!! . . .Just remember the machine is only as good as it's weakest link so even if you fit C1 ground screws they won't take up any slack in other weak areas so it could easily become wasted money. The goal and secret to a great machine is a balanced machine, if your going to fit C5 level then the rest of the machine needs to be built to C5 level.
    -use common sense, if you lack it, there is no software to help that.

    Email: [email protected]

    Web site: www.jazzcnc.co.uk

  3. #13
    Quote Originally Posted by JAZZCNC View Post
    Grease them when your ready to use the machine, there is enough grease inside them for setup etc but not enough for running.
    The stiff and notchy feel is quite normal, when greased and in use under weight they run smooth.
    Thanks for the confirmation!

    At 800mm your at the limit of a single screw and personally I would use twin screws, esp if using servos.
    Regards the screw size then it depends on the length, if over 1100mm then I would use 2020 with a 2:1 ratio, again even more so if using servos because of the higher RPM's servos run at. The ratio will half the screw speed but bring the resolution and federate back inline with 10mm pitch.
    If between 1000-1200mm You could use 1616 and do the same but the difference in cost isn't worth taking the trouble, and if over 1200mm then 20mm is the best choice.

    Just getting C5 rolled screws over C7 is worth it and ground goes a step higher but so does the cost. End of the day it's down to how a good a machine you want and your budget. BUT.!! . . .Just remember the machine is only as good as it's weakest link so even if you fit C1 ground screws they won't take up any slack in other weak areas so it could easily become wasted money. The goal and secret to a great machine is a balanced machine, if your going to fit C5 level then the rest of the machine needs to be built to C5 level.
    Looks like 2020 and dual screws are in my future! Will shoot Fred a message to ask about pricing on a couple of ball screws with bearings, which I'll mount inside the base up against the 8080 profile. And try to find someone local who can help me machine the frame end pieces to fit the two new ballscrews and add mounts for a pulley system with the motors inside the base, which should save a fair amount of room. I'm also having a bit of a sketch to see if I can mount the Y axis motor so its on the T extrusion I'll add to the back of the gantry to stiffen up the top. Although that will probably be a more long term plan since it would probably require replacing the screw - I don't think the end extends past the side enough to mount a belt pulley...

    I think one of the biggest potential areas where there's a risk of loss of precision is the X axis (longest rails, 1200mm) which are mounted to unmachined extrusion. The base face plates have two accurately machined notches that the rail ends rest in, however, so I figure I'll use those as reference points for vertical and horizontal alignment at the two ends. The Y and Z plates are flat and have machined surfaces and edges the rails can mount to, so that's much less of a concern/challenge for now.

    Also, anyone have a tip on what timing belts and pulleys are appropriate for this kind of build? Or a good source of basic info on the upsides and downsides of various systems (eg T5, T10, AT5, AT10, HTD??). Even just some photos of a 2:1 geared drive system on a DIY machine would be helpful...
    Last edited by Mattia; 10-07-2020 at 02:34 PM.

  4. #14
    Joined late so just my summary thoughts.
    One of my early machines was 600 wide and used a single screw and you could push each end of the gantry back and forth noticeably. I tended to cut in the centre line to hold a tolerance. So anything over 600 would be a double screw for me.

    I used T5 belts on an earlier machine but use exclusively HTD 5 now. I prefer the tooth profile on HTD and believe the shape is optimised for high torque.
    It has been a while since I looked into it but it think the AT types are somewhere similar in profile but I find the HTD work well.

    Although I’ve only ever used rolled screws I have never found them to be anywhere close to being a limiting factor on the overall machine. So in my view rolled threads can be used and still make a very good machine.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  5. #15
    Thanks all! I've dry-assembled the Z axis, didn't get around to the other two just yet. Looking and feeling good so far. I've been dabbling with Fusion360 (not quite 'got' it yet, but working on it) trying to come up with a design for mounting a pair of 200w servos for the x axis (on the assumption that two 400w servos for a gantry this size would be rather overkill).

    What I'm considering is mounting two 2020 ball screws inside the frame alongside the extrusion, face mounted to the end frame pieces using FK/FF mounts, having the lock nut on the fixed end recessed into the frame. Then mount a 40 tooth HTD5 pulley on the ballscrew. The idea is to find someone who can machine the end frame for a recessed 60mm motor mount with elongated bolt holes to allow for tensioning the 20 tooth pulley on the motor.

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    The way I've sketched it now leaves 7mm thickness for the motor bolts, with a 3.5mm recess for the round flange surrounding the motor's shaft. I'm guessing I should oversize the slots and recesses somewhat since it doesn't need to press fit in place and I'm not sure how tight the tolerances on the average 60mm frame motor are (0.5mm per side, or total? Suggestions welcome). Will this leave enough meat for the motor? Would 5mm be enough as well? How long would you leave the slots for belt tensioning? I've gone with 6mm slots for M5 bolts that are 16mm long. Too much? I'm a little concerned about the clearance at the edge of the hole to the recess for the plate around the shaft. Also need to work out exact positioning for this so the belt preferably does not run across the bolt caps, though an offset mount would mean less leeway in terms of taking up belt slack. Comments on this plan welcome. I'm also wondering whether to start a separate build thread or just keep all the questions here - I'm finding the dialogue very helpful in making decisions!

  6. #16
    So I've dry-assembled the gantry (all the mechanical bits except for the currently missing X axis ballscrew(s)). I was hoping I might be able to convert at least the Y axis to 2:1 belt drive as well (placing the motor on a bracket on the to-be-built gantry brace) but the ballscrews I have feature some pretty non-standard machining. Both ends are simply turned down with a retaining C-clip in a groove on the floating end, which is a nice snug fit in the holder; the fixed end is apparently only 'locked' in place by the flexible coupling, no retaining nut of any kind. Since the coupling can't fit through the machined holes as is (the bolt stick out just a little, need to file a small corner into the frame so it can pass), the Y axis is particular simply slips back and forth. The fixed ends do have a tapped hole in the end. Not very reassuring in terms of being able to adjust for backlash.

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    Thoughts? I guess this works well enough considering there are quite a few of these machines floating around out there, but it isn't super reassuring. I'll use 'standard' FK/FF machining and supports for the X-axis. But I may request a quote for a new Y axis ballscrew at least.

  7. #17
    Dag Mattia!

    How is your project going??

    Would be glad if you could advise on following...

    - Did you opt for a C5 screw?
    The thing is, Damen only offers C7 screws. Is that because you can even out the tolerance in software? But I guess t makes sense to get C3 bearing blocks to get rid of bearing backlash?

    - Are you happy with the 10mm pitch / lead?
    - Is it recommended to use a double ballscrew nut on 1200mm length? Dameter 20mm?
    - Did you pay any customs fees when ordering from BST?

    Thanks in advance!

    Greetz
    poldi

  8. #18
    So, time to revive! Sorry for the no reply Poldi, life and lack of funding got in the way again. I’ve spent the time actually designing some models (guitars) I can cut, so that’s an extra push to get this done.

    I’ve got the servos hopefully arriving tomorrow - 4x 400w deltas, 2 for Y, one for X, one with a brake for Z. Plan is 2:1 belt drive, 15mm HTD5 belts.

    I’m revisiting the Ball Screw issue now the motors are locked down - will likely get rolled C5 TBI ball screws from Fred at BST. The question is: 2020 and 1620 for Y and X, or 2010/1610?

    The motors can hit 5000rpm, but are in their optimum range up to 3000rpm. This would yield a theoretical maximum of 15-25m/min for 10mm, or a whopping 30-50m/min for the 2020 screws, juuust within the critical speed for screws that size (lengths 1200 and 790mm, as a reminder). With the 17 bit encoders and the fact I will mostly do wood, I’m not particularly concerned about accuracy for either - I do need to do accurate fret slots, but figure this should still be more precise and repeatable than my slotting templates and a saw.

    What I can’t quite estimate is whether the frame (with a slightly beefed up gantry) will be able to handle the super speeds of the 2020 option, and whether I may be better off with the still really more than fast enough 2010 option at these dimensions, sacrificing ultimate speed for better acceleration for possible 3D carving in my future. Or is there so much excess torque (spec’d at 3x baseline, so 3.8 NM @ 3000 rpm, but tailing off rapidly above that) that the speed gains are worth it, and design for the option to swap to 3:1 gearing in the unlikely event I want an in between option? For the Z, I’m guessing 1605 is plenty quick even with 2:1 belt reduction.

    The main use will be guitarmaking (bodies - mostly arched tops - necks, inlay, acoustic bridges, fret slots and jigs/tools/templates). Maybe light metal milling (brass, aluminum) for jigs and for prototype guitar hardware. I will likely also do some sheet good cutting for smallerfurniture projects, and want to dabble with some V carving/3D carving as well. With the ample power I’m pumping into the machine, what would you guys go for in terms of XYZ pitch?

  9. #19
    Small bump.

    Motors have arrived! Shiny! And HEAVY. Will wire them up for a quick test this weekend or early next week (time permitting).

    I’m the meantime, anyone care to weigh in on the ballscrew sizing issue? Going to shoot Fred a message soon to get a quote, since I’ve got the plans for the small amount of extra machining/brackets needed for the servos worked out now…

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