timing belt instead of lead screw

[baccus61]

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]

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]

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]

[/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]

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]

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. 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]

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. ..

[JAZZCNC]

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. .

[motoxy]

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. .

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

[Swarfing]

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......