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View Full Version : timing belt instead of lead screw



deannos
07-01-2012, 09:17 PM
I have seen and read posts about using a belt drive on the X axis instead of leadscrews. But not seen anything which says how good or bad it is. Is this any good, i'm looking at about a 48" axis

Swarfing
07-01-2012, 09:25 PM
Deannos i have two HTD5/15 belts on my router for the X and it works very well. For the time and effort though and doing it again i would go for the screw option. I still may upgrade them to screws at some point anyway.

deannos
07-01-2012, 09:29 PM
Deannos i have two HTD5/15 belts on my router for the X and it works very well. For the time and effort though and doing it again i would go for the screw option. I still may upgrade them to screws at some point anyway.

Hi, have you any pics of this please. I thought it would be easier to use belts. Are they looped belts or fixed at either end, i was thinking of using the latter. It also looks like it will be a lot cheaper

Swarfing
07-01-2012, 09:37 PM
I used open ended belt and it is bloody expensive and by the time you have added the pulleys?????? You need to be careful which type you use as well because of the stretch you get from rubber belts. There are some pics on here from when i was trying to set the steps up in EMC2. Do a search on my posts

deannos
07-01-2012, 09:50 PM
I was looking at the prices on here and they looked reasonable

http://www.beltingonline.com/

Swarfing
07-01-2012, 10:07 PM
For 6 metres it will cost you 120 quid. plus you will need other belts to get you geared to the right torch. I would not run these direct drive (way too fast) and for the money you could get 2 screws. I got mine from ERIKS which where cheaper but like i say by the time you add everything else it costs way more.

deannos
07-01-2012, 10:24 PM
For 6 metres it will cost you 120 quid. plus you will need other belts to get you geared to the right torch. I would not run these direct drive (way too fast) and for the money you could get 2 screws. I got mine from ERIKS which where cheaper but like i say by the time you add everything else it costs way more.

ouch, back to screws then.

Thanks

Jonathan
07-01-2012, 10:38 PM
Belts... advantage is less power required to achieve higher acceleration and speed (since kinetic energy of moving belt and pulleys is much less than a long rotating screw). For a long axis it should be a lot cheaper since you don't need as high torque stepper motor (unless you use a rotating ballnut like I did, then you can still use the small stepper, but that's completely irrelevant for an only 48" axis).

Disadvantage of belts is, as 2e0poz said, they stretch. Any belt will stretch, it's just some are more stiff than others. Different tension members, cross sections/pulleys all make a differenc. To get reasonable resolution (and thus accuracy) from a belt it is apparent you need double reduction to get the right ratio from stepper to belt. That's more pulleys (expense) and more belts to stretch! Due to the stiffness I doubt you would be able to cut aluminium with belts, whereas you could with a ballscrew or another type of screw.

That does however make belts great for something like a laser cutter or rapid prototyper where there are no cutting forces and the accuracy is not so critical.

baccus61
02-03-2012, 03:13 AM
I have tried most of the forms of transmission out there and if you can afford it then get the ball screws or even a good anti backlash lead screw. The anti backlash lead screws are still good value for money and the polyacetal nuts are very good wearing. I have a 12 start leadscrew on my x axis and its great. Fast rapids and pretty good control when geared down about 3:1 on the motor.
A lot of people make their routers very accurate but if you are only cutting wood then it needn't be as wood swells and contracts with moisture in the air. It's only the positional accuracy that you need and not resolution. i.e it has to come back to the same spot all the time (no backlash or looseness in the mechanism).
I went from belts to leadscrews to ball screws over a year or two so it would have been cheaper right from the start to get the ballscrews and have a good machine from the get-go. if you want a machine to last for the next 10 years or so then go ballscrew or anti backlash leadscrew.
Some of the Chinese ballscrews are very cheap but you need a press and lathe (or Vee block with indicator) to straighten them out when you get them as they are like spaghetti and are all over the place. I don't have a preference for either but the leadscrews with polyacetal nuts are better in a dusty environment. I have ballscrews on my Y axis (long) and to keep the dust out I loop a leather bootlace over the screw twice with a 3/4" nut hanging off the bottom of it to add some weight and do this on both sides. It wipes the screw before the nut goes over it and keeps 90% of the crap out of them. I grease the screws and don't oil them. I also have a fairly good dust extraction system which I think for a wood router is absolutely necessary not just for the machinery but for your lungs.
Here in Australia a few years ago the Gov health agency listed ALL Australian hard woods as being carcinogenic. This would probably be the same for a lot of woods in other countries as well. It makes sense to combat this problem at the source and not later through medical situations. Prevention is better... Blah, Blah, Blah, as they say.
Don't get single start leadscrews as the rapid traverse is just not fast enough. It's good for a metal machine for cutting but not a wood router where you need rapid repositioning. Get something in the way of 4 start or 20mm per rev (3/4") and gear down your stepper to about 3:1. I wouldn't go under 10-15mm per rev as it just too slow.
Steppers work stronger and better at low revs and if you have 8-10 microstep drives then the accuracy is as good as you need.
I hope this helps you out somewhat.
If you want toothed belts then the only ones I would recommend are the TDH belts or the ones with the rounded tooth profile as they seem to fit better than the sloped sided ones. (Most photocopiers I pull apart have TDH belts so the manufacturers can't be wrong) I have bought most of the type of belts on the market and the rounded ones definitely fit the best. I only use the belts on fast moving stuff now like a laser head etc that has little mass or weight to push around and I use leadscrew or ballscrew for the rest.
Ultimately it come down to what you can afford but my recommendation is to go with a screw type of setup.
Richard.

JAZZCNC
02-03-2012, 11:37 PM
Some of the Chinese ballscrews are very cheap but you need a press and lathe (or Vee block with indicator) to straighten them out when you get them as they are like spaghetti and are all over the place.

Not very fair that comment.!! I have bought literaly dozens of ballscrews screws from China and only 1 was ever so slightly bent and twenty minutes later straight.

baccus61
03-03-2012, 01:43 AM
Thanks for your reply.
I have bought 3 ballscrews from China and all were bent and needed straightening. This was from 2 different suppliers. What's not fair about telling the truth?
Were your screws short or relatively long?. Mine were 2x16mm x 1.25M long and one was 600mm long.
The smallest bend was about 0.012" and the largest was about 0.120. Way off line for a ballscrew.
This is my experience with them. You obviously have had a much better one.
I use the ballscrews about once a week and have had no trouble with them but I also don't push them to their limit either. Only on a wood router and small metal lathe.
They all were VERY cheap compared to what I can buy in Australia so you get what you pay for. It took me about 1 hour each to align in the press and swap out to the lathe to check alignment and they are now about 0.005" true along the whole length.
I'm happy with the price and happy with the end result BUT only after a bit of work here at home.
If your supplier has sent you good ballscrews then post the name here so others may buy nice straight ones from them so they don't have to go through the process of truing them up. I have a pretty good workshop and, from what I have seen here on this forum, others may not.
I'ts just my opinion from my experiences.
Rich

JAZZCNC
03-03-2012, 09:14 PM
Thanks for your reply.
I have bought 3 ballscrews from China and all were bent and needed straightening. This was from 2 different suppliers. What's not fair about telling the truth?
Were your screws short or relatively long?. Mine were 2x16mm x 1.25M long and one was 600mm long.


Sorry buying just 3 screws and deducing from this that all chinese ballscrews are rubbish hisn't fair.!!
I've bought lierally dozens ranging from 250mm to 1800mm in length in all sizes and in my experience they are very much ok and only had 1 screw bent and one that was machined badly.

It's no secret where I get my ballscrews from and I'm always recommending and saying they come from Chai at linearmotion bearings, I've also bought several spindles without issues thou I do recommend staying clear of the VFD's.

I agree they are cheap and you get what you pay for but they are more than good enough for DIY. Yes there will be bent screws just like there are fault spindles and VFD's but in the grand scheme of things and considering the numbers they must sell I think the overall percentage will be low.!
Saying all chinese screws are like spaghetti is incorrect, Others read this and are put off from buying from china and here in UK this can severly up the cost of building a machine.

Gud day. .:wave:

Robin Hewitt
04-03-2012, 12:07 AM
If you can stand a bit of cogging, sprocket and chain is quite cheap and works happily under enormous preload.

I saw a huge Russian gantry mill as few years back that was drawn by chunky spring steel bands.

Plotters are often driven by steel cord wound round a spiral pulley.

baccus61
04-03-2012, 12:54 AM
[/QUOTE]
I agree they are cheap and you get what you pay for but they are more than good enough for DIY. Yes there will be bent screws just like there are fault spindles and VFD's but in the grand scheme of things and considering the numbers they must sell I think the overall percentage will be low.!
Saying all chinese screws are like spaghetti is incorrect, Others read this and are put off from buying from china and here in UK this can severly up the cost of building a machine.

Gud day. .:wave:[/QUOTE]

Point taken.
But, How many people here will buy dozens of screws for their small home built machines. Not too many I think. This is my experience and I have commented on what I ended up with. I won't lie and say the screws were all within 2 microns of parallelism. It's like me saying Arsenic is good for you.
I have also bought 2 VFD's from China with the associated spindles and haven't had a problem with them. Does this mean now I need to stay clear of them because you have had a bad experience with them. Not at all. For the price I will continue to buy them until I run out of money or things to make. Compared to running a very noisy wood router the VFD's are in a world of their own and now my neighbours don't complain. :-) I love 'em.

All I can do is post MY experiences here so others may be more aware of what to expect. Very doubtful it will stop them from actually buying them due to how cheap they are

I will still buy the ballscrews from China as they are very cost effective for my needs and if I have another slightly bent one I will straighten it. It doesn't take long but really isn't something I should have to do with a precision part.

I won't continue to hijack this thread as I have had my say. Thanks for your informative opinion and foresight.
Richard.

Jonathan
04-03-2012, 02:28 AM
Not very fair that comment.!! I have bought literaly dozens of ballscrews screws from China and only 1 was ever so slightly bent and twenty minutes later straight.

I've only had 10 ballscrews from Chai but were all straight and fine, including the 2m long 25mm screws. Not actually measured how bent they are as that's easier said than done to do accurately, but I've not had any problems with them.


But, How many people here will buy dozens of screws for their small home built machines. Not too many I think.

That's not the point ... Jazz and I have bought 'dozens' between us only had one bent screw. So the probability of getting a bent screw is one in dozens which sounds good to me for the price. Even if you buy them from Zapp they may still be bent, as happened to someone on this forum long ago. I guess your parcel unfortunately got something very heavy put on top of it in transit which bent two out of three screws.

One thing to consider is I bought 4 of my ballscrews with the linear rails as when the ballscrews are bundled together with the rails that will strengthen the package and make them less likely to bend in transit.

I've got 2 of the VFDs and the only problem I had was my own fault for not securing a wire properly. They're both working fine now on the lathe and router.

baccus61
04-03-2012, 08:23 AM
Hi Jonathan,
Thanks for contributing.
Do you use the screws for machines you build at the Uni? or do you use them for home use?

2 out of the three screws I had were bent in about 4 places along the length (think sine wave) so something must have bounced on them repeatedly. I also haven't said they are rubbish either. If an individual that doesn't have too much money, like a lot of people building their own machines on this forum do, then they may have to save up for a long time to buy them. I just hope they aren't disappointed "IF" they are bent. The ones I bought also came from Linearmotion Bearings on eBay. I will still buy from them if the need arises which probably will when I build my 5 axis router next year. The good thing about Linearmotion Bearings is they will make any length of screw you need as long as the pitch is 5mm or 10mm. Maybe they have some newer machinery now and can make other pitches but when I asked them, about 1 1/2 years ago, they said they only do those 2 pitches.

I would love 25 to 30 millimetre pitches on the smaller screws so I don't have to spin them as fast for positioning. I have a 12 start 1" on my X axis on the router and it's great. It's an anti-backlash polished acme thread. I've had it for about 3 years and hasn't seemed to have worn any noticeable amount in that time. I lube it every time I use it with a couple of drops of 3 in 1 oil.

A few years ago I bought a ballscrew from the USA from McMaster Carr ( VERY inferior to the Linearmotion ones and which would probably be better used for a jack screw) and when it arrived from FedEx it had a 90 deg bend in it at the top 1 foot down. This was a hardened steel 5/8 screw. It must have had a car fall on it or something. I was able to return it for a replacement which took about 1 week to arrive. Maybe that was the case with the other ones. I'm not a clairvoyant so I can't answer that. :smile: I can see Jazz's point too if he is selling the product. He obviously wouldn't want any negative things said about them which would impact on his profits.

The easiest way I have found to measure the run out of the ballscrews is to use the nut as a gauge and keep it from turning so it rides along the ballscrew and select the pitch of the leadscrew on the lathe to follow the same pitch of the ballscrew and use an indicator on the ground part of the nut. There will be some minute discrepancies with the pitch's but measuring where the balls ride it is much better than measuring across the outside where all the deformation is after the rolling process. Sounds harder to explain than to do it

To Robin,
I use chain drive in my plasma table build and have found that if you go over about 18tpi then the cogging effect is reduced tremendously and seems pretty smooth. I gear down the stepper with 5/8 wide TDH belts 3 or 4 to 1 then drive the roller sprockets with the chain. It's actually pretty smooth and I only have problems with chain stretch or bounce if I go over about 8meters/min in speed. You have to adjust your acceleration to suit as well.
I used the chain drive selector on the Renolds Chain selection chart and mine will last 35 years without lubrication. I guess it will be a lot less than that after all the plasma dust works it's way in. It's very cost effective compared to rack and pinion. If you can afford rack and pinion then I would use them as there is zero bounce with that setup. It's just so darned expensive.

Richard.

JAZZCNC
04-03-2012, 11:32 AM
Point taken.
But, How many people here will buy dozens of screws for their small home built machines. Not too many I think. This is my experience and I have commented on what I ended up with. I won't lie and say the screws were all within 2 microns of parallelism. It's like me saying Arsenic is good for you.


Bloody hell not often Jonathan and me agree but he's spot on..:tup: . . . You completely missed the point.! This is not an attack on you personally more on the results of your comments.!!

Nobodys asking for lies and I appreciate the dissapointment when things arrive damaged but comments like "spaghetti screws" does put people off. I know this for a fact because I get absolutly loads of folks contacting me asking for advice or re assurence because they've read comments like this which then muddy's the water and sends there brains into melt down.!!
It's like my comment about the VFD's, yes in reply to you I haven't said this because it wasn't the matter of the subject, but when folks do ask I clarify why I'm not keen but I also say say they work fine if you get a good one.
To be honest my point of view regards them is changing because they seem to be getting better, but in the early days it was a lottery if you got a good one and if you did how long it would last.? Also the price differnce between buying one without or one with VFD has gotten so small it's a chance worth taking. (Thats why I've just ordered 2 sets.!!)

I also wouldn't expect anyone buying cheap ballscrews from china to expect tolerences down to sub micron level just like I don't expect you have them down to that after you got them straight-er.!!
You get what you pay for thats for sure but if what you get is good enough for the job then happy days. .:toot:.

JAZZCNC
04-03-2012, 04:36 PM
:smile: I can see Jazz's point too if he is selling the product. He obviously wouldn't want any negative things said about them which would impact on his profits.

You obviosly don't come on here often because if you did then you'd know I don't sell anything.!!. . . . I help others build machines pritty much free of charge often only profit involved is beer money. . :beer:

motoxy
04-03-2012, 05:28 PM
You obviosly don't come on here often because if you did then you'd know I don't sell anything.!!. . . . I help others build machines pritty much free of charge often only profit involved is beer money. . :beer:

Aww he's such a nice wee laddy.:heehee:

Swarfing
04-03-2012, 11:29 PM
Go for screws, if it is small machine then have a go at belts as does work very well :-)..........glad i stayed out of that one for once......

baccus61
04-03-2012, 11:30 PM
Well, That was a healthy discussion. Maybe I should have just said ...uncooked spaghetti and saved you some time. Maybe also I can get some beer off you one day. I will stand corrected on this one and slink back into the corner. It would also be nice if some of the 600 or so people that have read this post would contribute as well. :-)

Your right, I don't come here often but I do like the threads here and some of the machine builds are very clever and VERY well made. I think when I joined up I was member #86 but didn't come back very often as there wasn't too much on here that interested me at the time then the site underwent an upgrade and all my previous posts were lost. No big deal really.

SO, back to the original point of this thread, what do you recommend?

Swarfing
04-03-2012, 11:33 PM
How comes my answer is above yours? when i answered it afterwards?

baccus61
04-03-2012, 11:58 PM
I had a double post and edited it out probably at the same time you posted. :)

I made a small wood router years ago with 1/4" wide belts and size 17 steppers that had an area of about 12 x 12 inches and they worked very well. the spindle was a model plane brushless motor with a small fan on top to keep it cool while it spun. I didn't notice any stretch on the belts and probably wouldn't with the small motors.

JAZZCNC
05-03-2012, 06:22 PM
Well, That was a healthy discussion. Maybe I should have just said ...uncooked spaghetti and saved you some time. Maybe also I can get some beer off you one day.

Can't beat a good healthy disscusion and if You pay my plane fair, I'll buy the beer and we can discuss CNC machines untill you passout.!!. . . . Erm hold on thou your an Oz'y so it may be cheaper tother way round.:beer:

Ok then back to it.!!. . . Think I've said this before.?? I've built a few small belt machines and they work great if correctly sized pulleys and ratio.!. . . .BUT . . . with experience it really doesn't workout much cheaper than buying ballscrews from china and the difference is night and day.! . . . . . So I vote can't beat a good screw..:naughty:

JAZZCNC
05-03-2012, 06:24 PM
Go for screws, if it is small machine then have a go at belts as does work very well :-)..........glad i stayed out of that one for once......

Your just going soft. . .:joker:

Swarfing
05-03-2012, 08:55 PM
Just call me cheese :exclaim:

JAZZCNC
05-03-2012, 10:36 PM
Just call me cheese :exclaim:

Ok then your a "Stinking bishop". . :tup:

Swarfing
06-03-2012, 12:03 AM
ok Cheddar less of the bishop:lmao:

baccus61
06-03-2012, 08:25 AM
Well Jazz, if you want to have a beer with me then I'll meet you in Antarctica next year on Feb 11. I'll be on the Antarctic peninsula. Don't worry about the ice box as I think it will be cold enough......and it will be room temperature. Just the way the UK likes it. I don't drink too much now as I'm too old for that but 30 years ago I might have given you a run for your money.

How do you keep the crud out of the ballscrews? It's something I have had a lot of thought on over the years. The leather strap/thong draped over them with a weight seems to get 90% of the stuff away from getting caught up in them.

Thank God for the Chinese and their cheap parts. It makes our hobby just that much more affordable. Ten years ago when I started building CNC stuff there wasn't much second hand stuff around and I wasted a lot of money buying stuff I thought MIGHT do at a pinch. Most of it is still sitting in the tool box and cupboards. There has been no better time to build CNC machines than now and also with the American dollar at an all time low and the market being flooded with new parts for second hand prices. I am jealous. The advent of all these Forums has also helped tremendously.