leadscrew vs ballscrew
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@Dad003 said in leadscrew vs ballscrew:
20<60,20<60 ,
i think it will give you 240 steps. (assuming 1.8 steppers)
you have twice a 3:1.
your actual belt to move the z is 60 tooth.
so 200/2/60* 1/16 microstepping 26.66
3:1 once is 80
3:1 twice is 240
the solution on the ender 3 is
16<80 which gives a 5:1 ratiothen use a 20 tooth to drive the belt.
200/2/20 * 1/16 microstepping = 80
5:1 with 80 is 400.
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Just to be clear- you are saying that your 'out of straightness' leadscrew is putting enough lateral load on the build platform to give you Z-banding issues ? That does not make sense.
What may be the issue is the elastic buckling of that REALLY tall slender column. Peek into this rabbit hole - https://en.wikipedia.org/wiki/Euler's_critical_load
There are other theories, but this is the easiest to understand.Some quick and dirty estimating to put it in perspective- the normal range for compression members, we proportion them to a ratio of KL/r <200. For Tension members, we normally try to hole to KL/r<300. Since it a machine that we are try to get some manner of precision out of, I would not go over 80 in general.
A 700mm long TR8x8 leadscrew has an effective solid cross section of 6.5mm. This results in a KL/r of 461! Critical buckling load is about 17 pounds. This is kinda why TR8's dont scale well beyond i3 lengths. Look at the critical stress curve and about where i faked it in and plotted the resulting critical stress.
What might be an easier and faster mod to try and cure that is put the leadscrew in tension instead of compression. Use a stop collar and thrust bearing at the top and HANG the platform from above. Tension is self righting. You are mostly doing the same thing with a hanging belt drive, but adding ain a bunch of complexity with all the jackshafts.
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@CaLviNx Yes, I am completely aware of that principle and my first thought was exactly what you are talking about, but in practice making a floating nut in a dual z-axis setup like mine (the z axis is holding the x-axis bar) and a height of 500mm that made more problems than solve. When the leadscrews are very long (like mine - almost 600mm) and you do not align them perfectly - the nut and/or screw tend to "dance" a bit which translates into visible z print artifacts. Using a springy motor coupler with a small ball bearing inside) helped a little bit with the constraint problems. When I was talking about aligning - I was thinking more about aligning the linear rails - since I have 4 of them for Z - 2 for each side od the Z axis, and aligning 4 linear rails to do a constrained up/down motion together is a pain. Also it's much more difficult when the lead on the leadscrew is 2mm instead of 8mm which is more common on printers since it's much more sensitive to misalignment.
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@omni said in leadscrew vs ballscrew:
................ When the leadscrews are very long (like mine - almost 600mm) and you do not align them perfectly - the nut and/or screw tend to "dance" a bit which translates into visible z print artifacts.
If the linear rails are doing their job, and the screws are unconstrained, then any "dancing" of the nut or screw should not translate into any movement of the build platform. If it does, then there must be unacceptable play in the linear guides.
When I was talking about aligning - I was thinking more about aligning the linear rails - since I have 4 of them for Z - 2 for each side od the Z axis, and aligning 4 linear rails to do a constrained up/down motion together is a pain.
Which just means that you are using too many guides. You only need two, preferably located at opposite corners of the build platform. Located and aligned correctly, this is enough to prevent any movement in X, or Y and also any rotation.
Also it's much more difficult when the lead on the leadscrew is 2mm instead of 8mm which is more common on printers since it's much more sensitive to misalignment.
How so? How does the thread form affect the ability to align the screws? An 8mm lead, 4 start screw has the same 2mm pitch as a 2mm lead, single start screw.
For info, I use three unconstrained 8mm diameter 2mm lead screws, 900mm in length driven by a single motor and continuous belt, which raises and lowers a 400mm square build platform constrained by two linear guides arranged as detailed above. No Z artefacts, no need for any sort of software bed levelling or flatness compensation.
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@deckingman said in leadscrew vs ballscrew:
Which just means that you are using too many guides. You only need two, preferably located at opposite corners of the build platform. Located and aligned correctly, this is enough to prevent any movement in X, or Y and also any rotation.
EXACTLY!
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@omni said in leadscrew vs ballscrew:
@CaLviNx Yes, I am completely aware of that principle and my first thought was exactly what you are talking about, but in practice making a floating nut in a dual z-axis setup like mine (the z axis is holding the x-axis bar) and a height of 500mm that made more problems than solve. When the leadscrews are very long (like mine - almost 600mm) and you do not align them perfectly - the nut and/or screw tend to "dance" a bit which translates into visible z print artifacts. Using a springy motor coupler with a small ball bearing inside) helped a little bit with the constraint problems. When I was talking about aligning - I was thinking more about aligning the linear rails - since I have 4 of them for Z - 2 for each side od the Z axis, and aligning 4 linear rails to do a constrained up/down motion together is a pain. Also it's much more difficult when the lead on the leadscrew is 2mm instead of 8mm which is more common on printers since it's much more sensitive to misalignment.
All this says to me is: BAD DESIGN....
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@deckingman said in leadscrew vs ballscrew:
How so? How does the thread form affect the ability to align the screws?
you must constraint the screw in one point - motor ... so lets assume the other side of the screw is free for the screw tip to "fly around" on the top ( like most of mine design have) with "small 8mm screw and 4x2 pitch" the nut can handle a misalignment of e.g. 1 degree without binding. identical setup with bigger 10mm screw and 1x2 pitch nut "grabs" more threads and at 1 degree binds up, can handle max .2 degree without binding. Not sure why I'd have to draw them both to see why the bigger one binds so much at same angle... the ideal solution for this is with those arresters that ppl used to design where you allow nut to freely move in XY direction but you lock it in Z direction... I never tbh seen a design that I liked and used more than few
the angle I'm talking about if unclear is the angle between the center axis of the nut and the center axis of the screw
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@CaLviNx said in leadscrew vs ballscrew:
All this says to me is: BAD DESIGN....
as I'm familiar with that build ... it's of course way better design to use single high quality linear rail on each side of the X bar that moves in Z direction, but due to well known situation right now getting a high quality linear rail here is next to impossible and cost more than that whole printer so not really doable. That's why 2 smaller PRC linear rails are used on each side. Doubling them increases their precision / reduces the "play" but increases complexity of the alignment significantly. So the design is driven by what's available and not what's best
... took a while for omni to align those 4 rails and 2 nuts but that machine now works freaking awesome 
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@arhi said in leadscrew vs ballscrew:
the angle I'm talking about if unclear is the angle between the center axis of the nut and the center axis of the screw
Good design and proper assembly cures all.....
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@CaLviNx said in leadscrew vs ballscrew:
@arhi said in leadscrew vs ballscrew:
the angle I'm talking about if unclear is the angle between the center axis of the nut and the center axis of the screw
Good design and proper assembly cures all.....
fairly possible when you do it from scratch, not something you can force when you are retrofitting something like wanhao d9
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@arhi said in leadscrew vs ballscrew:
@CaLviNx said in leadscrew vs ballscrew:
All this says to me is: BAD DESIGN....
as I'm familiar with that build ... it's of course way better design to use single high quality linear rail on each side of the X bar that moves in Z direction, but due to well known situation right now getting a high quality linear rail here is next to impossible and cost more than that whole printer so not really doable. That's why 2 smaller PRC linear rails are used on each side. Doubling them increases their precision / reduces the "play" but increases complexity of the alignment significantly. So the design is driven by what's available and not what's best
... took a while for omni to align those 4 rails and 2 nuts but that machine now works freaking awesome ...All my rails come from an Ebay seller in South Korea Dy Global and are either good used or new old stock being Genuine from various manufacturers Hi-Win, THK etc, i usually contact him and just ask for what i want instead of trawling his site as he usually has stuff in stock that is not listed on his page on ebay. I have had 7 orders from him now and every order has been perfect.
He supplies with 72hr shipping via fedex to europe included in the rail price.
So the "excuse" of good rails not being available is horsesh**
The best rails I have had so far are Bosch-Rexroth, they just ooze quality you can see it and feel it from just holding them in your hands
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@arhi said in leadscrew vs ballscrew:
@CaLviNx said in leadscrew vs ballscrew:
@arhi said in leadscrew vs ballscrew:
fairly possible when you do it from scratch, not something you can force when you are retrofitting something like wanhao d9
For some games that you know you cant win, dont play......
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@CaLviNx said in leadscrew vs ballscrew:
So the "excuse" of good rails not being available is horsesh**
ah ... don't talk about stuff you can't even imagine
- 99% of amazon sellers will not ship to Serbia at all, no matter what shipping method
- fedex/dhl if/when arrive here cost us another 100eur for "customs processing"
- on top of price+shipping+customs processing we need to pay another 10% customs + another 20% VAT on top of all that
- in order to do "customs processing" we need to show proof that it will not be used in food production, weapons manufacturing and provide bunch other "import" paperwork + if customs decide on we have to pay for testing "quality" of the goods... laws didn't change much from Tito era and are made for big corporations to do all the import work and for private persons to be able to have access to only local stuff .. we use tricks to go around it but due corona most of those channels are dead now
For some games that you know you cant win, dont play......
when you know up front, yes, but when you are already waste deep .. you get it done any way you know how
anyhow, we are hijacking thread with irrelevant discussion
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@arhi said in leadscrew vs ballscrew:
@CaLviNx said in leadscrew vs ballscrew:
So the "excuse" of good rails not being available is horsesh**
ah ... don't talk about stuff you can't even imagine
- 99% of amazon sellers will not ship to Serbia at all, no matter what shipping method
- fedex/dhl if/when arrive here cost us another 100eur for "customs processing"
- on top of price+shipping+customs processing we need to pay another 10% customs + another 20% VAT on top of all that
- in order to do "customs processing" we need to show proof that it will not be used in food production, weapons manufacturing and provide bunch other "import" paperwork + if customs decide on we have to pay for testing "quality" of the goods... laws didn't change much from Tito era and are made for big corporations to do all the import work and for private persons to be able to have access to only local stuff .. we use tricks to go around it but due corona most of those channels are dead now
Try living on an "island" (Cyprus) that is technically in the EU but you get the age old line "cannot ship to your location" Then with couriers who wouldn't know what a decent days work was if it smacked them in the face.
For example: A Parcel Was picked up from a sender in Austria @ 16:00 Wednesday, it arrived in Larnaca (Via Germany) @ 13:15 on Thursday, but delivery is not scheduled until NEXT Tuesday........ So it can travel over 4000kms in just over 9hrs but the last 25kms it takes to travel from Larnaca to me is going to take over 4 days.....
Then there is DHL you pay more for DHL but DHL cheaps out and hands the parcel over to their "local delivery partner" and DHL's "local delivery partner" here is Cyprus Post Office and Cyprus post office is a funny thing they only have postmen in Four locations on the whole island, Larnaca, Limassol, Nicosia & Phafos in any other area there is NO postmen/woman, what they do is that you have to register your mobile telephone with them and when anything arrives for you, they send you a SMS and you have to go and collect so even if you paid more for DHL you still have to collect it. And as soon as DHL passes the parcel over to Cyprus post office, the tracking lists is as "item sent abroad" and from experience that means it arrives in Cyprus the very same (or next) day but tracking is never actually updated for 2 to 3 (usually 3) weeks saying the item has just arrived, and then once it has been listed as having arrived it usually takes 10 days to actually arrive at the local post office, so a thing you paid for to be sent on a 3 to 5 day service ends up taking over a month, DHL hate me as I make a claim for my cost of shipping EVERY time they do this.
Then we get on to the local mafi.. (sorry customs) they arbitrarily add a certain amount as a "service" charge to release items (even if it came from Europe) as and when they choose.
Then we get to the independent couriers who the likes of TNT and ARAMEX use, well they all deliver your "expedited" (read higher price paid) parcel to their "local office" and then again send you and SMS trying to get you to go and collect it from their local office instead of them actually delivering it to your door, I have an email/sms trail of 37 messages from a local courier company asking me to go and collect differing parcels, and every reply to them I tell them "NO deliver it" and the very next day (or two) they do deliver it, but if you let them get away with it they will try to save money by not doing their job.
Then you get the age old excuse "I cant speak English" to try to avoid doing anything, i either do one of two things, if im with someone i turn to the person im with and insult the person in english, that person who just said they couldnt speak english, if they react, i reply oh I thought you said you couldnt speak english.... if im on my own i reply to them in Greek, as i can speak it quite well.
So yes horsesh** everyone all over the world has their own set of circumstances to overcome, so the line :
"ah ... don't talk about stuff you can't even imagine
"Doesn't wash with me.
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@arhi said in leadscrew vs ballscrew:
................. 10mm screw and 1x2 pitch nut "grabs" more threads ..............
No it doesn't. A four start screw with 8mm lead has a pitch of 2mm which is exactly the same pitch as a single start screw with 2mm lead. The number of threads from peak to peak engaged with a nut is exactly same in both cases.
I'll concede that the helix angle is different though - that might make a difference. But if one cannot align a lead screw that is only constrained at the motor end, within the amout of "float" that any nut will give, then one should not attempt to build a printer, but take up another hobby like knitting perhaps where it wouldn't matter if the socks turned out a bit wonky.
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@CaLviNx said in leadscrew vs ballscrew:
Try living on an "island" (Cyprus) that is technically in the EU but you get
6 months in 2003 in Nicosia
4 years after that in Lemessos (50m from Castle hotel, next to the go-cart track)Was CTO of PlanetSky :D, was shipping dvb cards from Cyprus to whole EMEA, shipping servers trough EMEA, getting sat eq. to Cyprus ... the pain... I still feel it
It is not as bad as here but yes, you know the pain of "won't ship", I retract the "you can't even imagine"... damn, yes you can ..
... So it can travel over 4000kms in just over 9hrs but the last 25kms it takes to travel from Larnaca to me is going to take over 4 days
I can show you tracking info where stuff arrives to the Belgrade post office in under a week and then it takes 2 months to go through customs and arrive to my home... and that's not a "special case", it's rather "normal" .. it's the reason Aliexpress killed "free shipping" and "cheap shipping" for most stuff to Serbia and only fedex/dhl works now.
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@deckingman said in leadscrew vs ballscrew:
No it doesn't. A four start screw with 8mm lead has a pitch of 2mm which is exactly the same pitch as a single start screw with 2mm lead. The number of threads from peak to peak engaged with a nut is exactly same in both cases.
nope because the 10mm nut is bigger... I'm not sure how they make them but I suspect it's some relationship between diameter and height so the 10mm nut is higher than 8mm nut but good 30%
I'll concede that the helix angle is different though - that might make a difference.
no idea, maybe that makes difference, as I said it's just observed that the 10x2 handles less angle than 8x4x2 ... I never got too much into reasons, just the fact that nut is longer explains it partially
But if one cannot align a lead screw that is only constrained at the motor end, within the amout of "float" that any nut will give
These nuts don't give at all, the tolerance is crazy tight, but as said, it took a bit of trial and error and 4-5 tries but it was aligned properly and now works awesome. It is just mentioned 'cause compared to 8x4x2 the 10x1x2 was a lot harder to align ... not impossible, just harder ... 8x4x2 took no effort, 10x1x2 took a whole day
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@arhi said in leadscrew vs ballscrew:
nope because the 10mm nut is bigger... I'm not sure how they make them but I suspect it's some relationship between diameter and height so the 10mm nut is higher than 8mm nut but good 30%
But the OP was comparing the just the lead. His exact comment was (quote)
"Also it's much more difficult when the lead on the leadscrew is 2mm instead of 8mm which is more common on printers since it's much more sensitive to misalignment."
He made no mention of different diameters. That's what I was commenting on. Of course a bigger screw and bigger nut will behave differently but that's not what the OP said.
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@deckingman said in leadscrew vs ballscrew:
He made no mention of different diameters. That's what I was commenting on. Of course a bigger screw and bigger nut will behave differently but that's not what the OP said.
omni uses bigger screw (10x1x2) and mentioned how harder it was to line up and you replied to his post
.. all clear now -
@CaLviNx said in leadscrew vs ballscrew:
mind you i have a few years of experience of straightening hydraulic rods offshore.
that might be it!
