Designing a reliable and accurate Z axis. May 22, 2015 03:06PM |
Registered: 9 years ago Posts: 63 |
Re: Designing a reliable and accurate Z axis. May 22, 2015 03:39PM |
Registered: 10 years ago Posts: 869 |
The one that doesn't move.Quote
FalloutBe
Which Z axis design is, in your opinion, most accurate, and thin in height
Re: Designing a reliable and accurate Z axis. May 22, 2015 03:47PM |
Registered: 9 years ago Posts: 63 |
Re: Designing a reliable and accurate Z axis. May 22, 2015 04:46PM |
Registered: 10 years ago Posts: 869 |
Look at a Makerbot Replicator or Ultimaker printer. They have a single leadscrew on the back edge with a cantilevered build platform. It all comes down to how that bracket supports the bed. With appropriate bracketing, multiple linear bearings orientated vertically, and/or multiple lead screw nuts, you can make the force appear that it's coming from the middle when it's really coming from the side. Or you can reduce/eliminate the effect of torsional forces on the build platform. The smaller and lighter your platform is, the easier this task is. If you had a 1m by 1m square Alumnium plate bed, you're gonna have troubles. But if it's something a little more reasonable, then maybe it's possible. The thinner and thinner you want the overall z carriage height to be the less support it will have.Quote
FalloutBe
I really thought that, putting that single rod at one side of the bed, is bad. I can't imagine how the bed would be well secured like that,
but I can't say that it is not possible because I never felt how strong such a design is. You say it has been succesful.
Re: Designing a reliable and accurate Z axis. May 22, 2015 04:59PM |
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Re: Designing a reliable and accurate Z axis. May 23, 2015 02:22AM |
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Re: Designing a reliable and accurate Z axis. May 29, 2015 06:31PM |
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Re: Designing a reliable and accurate Z axis. May 29, 2015 06:51PM |
Registered: 10 years ago Posts: 14,672 |
Quote
FalloutBe
"The one that doesn't move"
Haha, indeed (;
But Something has to move in the Z direction.
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FalloutBe
I'm quite stuck now with the idea of "really wanting the bed to be my Z axis" because I am really happy with how well the XY assembly performs.
Re: Designing a reliable and accurate Z axis. May 30, 2015 01:22PM |
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Re: Designing a reliable and accurate Z axis. May 30, 2015 02:24PM |
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Re: Designing a reliable and accurate Z axis. May 30, 2015 04:10PM |
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Re: Designing a reliable and accurate Z axis. May 30, 2015 05:12PM |
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Re: Designing a reliable and accurate Z axis. May 31, 2015 12:10AM |
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Re: Designing a reliable and accurate Z axis. May 31, 2015 09:45AM |
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Re: Designing a reliable and accurate Z axis. June 01, 2015 09:49AM |
Registered: 10 years ago Posts: 869 |
A standard bearing like a 608 can handle radial as well as some axial forces. As long as you abuse the bearings and limit the axial forces, you shouldn't have a problem with them. There are better bearings if you want increased axial loads such a double-row angular contact or tapered roller ball bearings but are less common and more expensive and may not be readily available in very small sizes. For small bearings like the 608, the axial load rating is usually approximately 1/4 the static load rating. A typical 608 has a static load rating of around 1350N (300lbs) so a axial load rating around 337N (75lbs).Quote
FalloutBe
I also need some kind of bearing, which can rotate but keeps the lead screw from moving up or down.
I have no idea how this kind of bearing is called, can someone tell me please? ^^
Re: Designing a reliable and accurate Z axis. June 01, 2015 10:27AM |
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Re: Designing a reliable and accurate Z axis. June 01, 2015 03:05PM |
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Quote
FalloutBe
- One bearing on each end of the screw, with nuts on the screw that push the two bearings apart. (like this example)
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- Two bearings on one side with nuts that push the bearings together. (like this), and an additional bearing on the other end, just to keep the rod in place.
(in this second example, ignore the motor. In my case it'll be belt driven somehow)
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I'd like to go with the second option, because it doesn't put any stress on the frame of the 3d printer.
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Are there other ways of mounting them?
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Do you think it is a good idea to put 8mm pulleys on the 8mm lead screw? Or is the actual outer diameter of the lead screw a bit less than 8mm?
Re: Designing a reliable and accurate Z axis. June 01, 2015 03:08PM |
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Re: Designing a reliable and accurate Z axis. June 01, 2015 10:57PM |
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Re: Designing a reliable and accurate Z axis. June 02, 2015 10:05AM |
Registered: 9 years ago Posts: 63 |
How about a lead screw?Quote
cdru
An 8mm ball screw will have a major diameter slightly less than 8mm. The usual way I believe is to step the shaft down, so for a 8mm lead screw, you may need to use a 6mm 626 bearing.
Like in my attached image, this stress will only be applied to the black block at the top.Quote
cdru
I'm not sure how you figure that. If the bearings are mounted to something, there's going to be stress.
Do you mean in between the nuts that move the platform, or in between the nuts and the bearings at the top?Quote
o_lampe
I´ve seen simple versions with only a spring between the nuts.
Re: Designing a reliable and accurate Z axis. June 02, 2015 08:28PM |
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Re: Designing a reliable and accurate Z axis. June 03, 2015 12:03AM |
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Re: Designing a reliable and accurate Z axis. June 03, 2015 09:12AM |
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Re: Designing a reliable and accurate Z axis. June 03, 2015 05:50PM |
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Re: Designing a reliable and accurate Z axis. June 03, 2015 07:52PM |
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Re: Designing a reliable and accurate Z axis. June 03, 2015 08:07PM |
Registered: 9 years ago Posts: 344 |
Quote
the_digital_dentist
There are two types of ball screws- rolled and ground. The cheapos are the rolled ones and specs won't be as good as the ground screws. The rolled screws (which is what the ones in the photo appear to be) might be adequate for z axis lift.
You might want to watch for ground ball screws and see what ebay turns up used.
Re: Designing a reliable and accurate Z axis. June 03, 2015 10:15PM |
Registered: 11 years ago Posts: 1,049 |
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cristian
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cozmicray
or laser measurement of bed movement and full feedback to moving mechanism.
May you post some link for such measurement tools?
Re: Designing a reliable and accurate Z axis. June 04, 2015 11:51AM |
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Re: Designing a reliable and accurate Z axis. June 04, 2015 12:19PM |
Registered: 9 years ago Posts: 344 |
Quote
FalloutBe
Thanks again cozmicray, for all your help (;
I'm going for the cantilevered platform, 4 bearings, 2 smooth rods and a single lead screw.
What do you think will be best?
[www.ebay.com] (delrin nut)
or
[www.ebay.com] (motor attached, regular nut)
or
[www.ebay.com] (motor attached, regular nut, coupler)
?
The delrin nut states to have much better resolution, and it is cheaper.
The regular lead screws all seem to have an 8mm pitch, which I think is too large.
Anti backlash nuts or regular nuts?
The sets on ebay don't have anti backlash nuts :/ Do you think it is necessary?
Gravity should keep it down, but my platform is moving downwards along the print, so it might stick.
EDIT: I want at least 20micron layers!
Re: Designing a reliable and accurate Z axis. June 04, 2015 12:29PM |
Registered: 11 years ago Posts: 1,049 |