Gantry to bed height.

[m.i.k.e]

Hi all, I am getting stuck now that I am coming to the details, I changed the rails from the front of the x-axis to the top/bottom and now I am worried about the z height and does the z-axis width look ok?
Thanks for looking - cheers mike.


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[JAZZCNC]

Ok well first off regards the rails then I'd split the difference and go with bottom rail on the front face, top rail on the top face. That way you get more gantry clearance but keep a better rail spacing than both on the front face.
Obviously this depends on how much gantry clearance you need and material thickness you want to work on. Remember to think about tool lengths, how you have drawn now then you may struggle with clearance when using larger drills on thicker materials. With these dimensions, your thickest material size will be 75mm which might seem fine until you want to drill a hole thru it with say a 10mm drill and find the drill length won't fit.

Second, the Z-axis is a little narrow at 160mm and I'd be 180mm as a minimum with 200mm being better. Basically the wider the bearing spacing the better, obviously you don't want to waste too much travel but your better spending a little more money on the extra rail, screw, etc than compromising the machine trying to squeeze the Z-axis to fit the rails.


Third, you could lose some of that tubing on the frame. If you are going to use diagonal braces, like on the sides then you don't need the vertical piece or even the horizontal piece. You could drop at least one of the 3 little vertical pieces also and just have two supports. You want to reduce the amount of welding that goes into the frame because each weld is a potential stress point that will at some point release the tension causing the frame to move.

[driftspin]

Hello Mike,


You have 153mm under gantry.
Also you need some type of sacrificial surface 18mm?

Let's say maximum of 50mm of tool stickout length, and 20 mm safe distance to avoid hitting clamps.

Doesn't leave much thickness for a workpiece.
Maybe only 50 mm or so.


Will you ever need a vise to clamp a workpiece?

Top of my big vise is +/- 100mm high.


I wasn't sure about all this and arranged for 210 mm free space between table frame to top z position.

Hope this helps to narrow down the choices you have to make.

Grtz Bert.


Verstuurd vanaf mijn SM-A505FN met Tapatalk

[m.i.k.e]

Thanks, Jazz/driftspin, all good info and make perfect sense - If I put the bottom rail on the front as Jazz suggests I will have about 200mm to the bottom of the gantry. I was going to build a height-adjustable bed but I was worried it misaligned when tightening the bolts up. I'd better get back to the drawing board lol.
cheers Mike.

[routerdriver]

I suggest you draw a line from the tip of your tool to the corner of the Z axis plate.This may illustrate the limitation you can encounter with taller workpieces-you can't get down the side of them.Its equivalent to what off roaders call approach angle.Won't be a problem if you intend to work on items in a vice but it looks like the design features a larger working area than just a vice would require.

I appreciate that isn't a totally finished design,but I can't quite understand which parts of the Z axis are moving as the mounting plate for the stepper sits on top of the Z axis backplate and no slots are visible.Will there be ballscrews or timing belts on the X and Y axis?One point to note is that if you go along with the sound suggestion of increasing the width of the Z axis to 200mm you will have a region of 100+mm either side of the machine that can't be accessed so make sure that the width is sufficient for the biggest part you are likely to be working with.

[m.i.k.e]

Hi routerdriver, Yes definitely not finished lol. The stepper plonked on the top may be moved behind the z backplate with pullies. Don't know whether you can make it out better in this image. Like you say the working space is disappearing quickly but I'd rather it be built properly.
cheers Mike.

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[m.i.k.e]

Hi all, here is the new design and I hope I have understood all the recommendations you advised. I don't want to start a build log until I at least have a clear plan.
This is design is based on -
y 1200
x 800
but I'm going to scale it up to -
y 1500
x 1000

The machine is hopefully going to be used for cutting wood/aluminum, the frame is 60x60x5mm steel, the A braces will be made of 60x4 round galv as I can get that for scrap (shown as square in the images) and the gantry 160x80 and 80x80 aluminum extrusion.
The rails/bearings cheap 20mm hiwin copies and ball-screws from Ali express.
The kit only comes with 300mm z rails which I'm not keen on but could be upgraded later (that's the downfall of getting a kit I suppose) I will keep looking for a better kit.
Any suggestions welcome :encouragement:
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[Voicecoil]

Another wee tip for you: check the info on the spindle you're going for as to where you're allowed to clamp it. I didn't and when I read the manual I found that my original idea of being able to slacken off the clamp and move the spindle up or down to allow the use of longer/shorter tools wasn't going to work 1/3 as well as I thought it would. Just because you have 150mm of Z travel doesn't necessarily mean you can machine something that's 150mm thick!

[m.i.k.e]

Cheers for that Voicecoil - I didn't know that, I'm going to look for another kit or order them separately. In the images above the Z height is 210mm which I think is a lot better. Cheers, Mike.

[JAZZCNC]

I see a classic mistake often made.!!. . . I will give you a clue but won't tell you what it is yet as a bit of fun test...Lol. . . . . If you don't see it then shout up but I think it will be obvious if you look carefully.!

"Fastenings" is the Clue.??

[JAZZCNC]

Hi all, here is the new design and I hope I have understood all the recommendations you advised. I don't want to start a build log until I at least have a clear plan.


No start one straight away. It's the best way then all your thoughts and questions are answered in one place rather than being scattered around the forum.
This is better for you and others following the thread because it can take several months or years for some people and you can easily go back and find info from months ago.

[Kitwn]

I see a classic mistake often made.!!. . . I will give you a clue but won't tell you what it is yet as a bit of fun test...Lol. . . . . If you don't see it then shout up but I think it will be obvious if you look carefully.!

"Fastenings" is the Clue.??

One of the reasons for mocking up the design in cheap MDF or plywood before marring the pristine beauty of your expensive aluminium plate.

[m.i.k.e]

One of the reasons for mocking up the design in cheap MDF or plywood before marring the pristine beauty of your expensive aluminum plate.

Sounds like a good plan ��

[m.i.k.e]

No start one straight away. It's the best way then all your thoughts and questions are answered in one place rather than being scattered around the forum.
This is better for you and others following the thread because it can take several months or years for some people and you can easily go back and find info from months ago.

Will do.

[m.i.k.e]

I see a classic mistake often made.!!. . . I will give you a clue but won't tell you what it is yet as a bit of fun test...Lol. . . . . If you don't see it then shout up but I think it will be obvious if you look carefully.!

"Fastenings" is the Clue.??

hi JAZZCNC, Is this the problem? bolting the Z bearing spacing block.

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[JAZZCNC]

hi JAZZCNC, Is this the problem? bolting the Z bearing spacing block.


No but your thinking along the right lines just in wrong place.?

[Clive S]

No but your thinking along the right lines just in wrong place.?

Put him out of his misery :sorrow:

[JAZZCNC]

Put him out of his misery :sorrow:

Nah I've got faith in him, he'll figure it out I'm sure and will feel better for it, plus I'm in whind up mood...:whistle:

[m.i.k.e]

I don't like this game �� ��

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[JAZZCNC]

I don't like this game �� ��

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Bingo.!!! . . . . But don't worry It's an easy fix and actually makes setup easier. You want another plate, basically, you make the gantry as two separate pieces. The bearing plate with ball-nut mount as one fixture and then have a separate plate on the gantry which bolts into the bearing plate. You will need to make the plates slightly wider than the gantry so can bolt them together.
The advantage of this setup is you can easily adjust the gantry square by losing the plates and it doesn't affect the ballscrews. The way you have it now if you needed to adjust the gantry square to the rails, which you 99.99% would need to do then any adjustment would have put twist on the ball-screws causing them to bhind.!

[m.i.k.e]

Yes Jazz that does make sense ��