Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: JohnHaine on September 06, 2012, 10:40:56 AM
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Hi folks, after a lot of thought I have decided that using plain screws on my lathe conversion is never going to give good results, and as far as I can see after a little experimentation I'm not going to be able to apply backlash compensation because the play in at least the Z leadscrew is too large. So, has anyone got any experience of replacing the myford screws with ballscrews please? Or could point me to info on the web?
I think I can see how to do it on the crossslide without too much trouble, but getting a long Z screw aligned with the nut on the saddle, and mounting the nut, has me stumped for now. Another problem will be protecting the screws from chips.
Thanks in advance!
John.
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Hi John,
I have been working on a similar project to fit a Southbend 9" with steppers and yes the leadscrew is the more challeging axis to eliminate/reduce the back lash. I choose to use low back lash nuts but often toy with the idea of ballscrews. Because I want to toggle between conventional and CNC use I will make due with poor mans method of backlash reduction. Maybe you should post a picture of your lathe, particularly the carriage & lead screw shot to stimulate some of our resident guru's ideas on how to interface a ball on the long screw. Picture says 1000 words or thereabouts.
Robert
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The wee lathe I am updating at the moment is based on a Myford ML10 so not sure if that will help or not.
Hood
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The wee lathe I am updating at the moment is based on a Myford ML10 so not sure if that will help or not.
Hood
That's a sweet baby retro project Hood!
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Yes its coming along nicely, just got started on it again the last week. I am going way overkill on it as I am testing out hardware that if it works out I will fit to the big lathe but this way is better as it keeps the big lathe intact and usable until I know for sure the new controller is working as it should,
Hood
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I have done two lathe conversions. I did use a ballscrew on both machines. Actually I did the conversion on a 9" SouthBend with the ballscrew mounts that I clamped onto the ways at the rear of the lathe. I removed all of the mechanisms at the front of the machine(apron?). It worked well until I acquired a Hardinge HLVH that was missing enough parts to make it useable as a cnc conversion only. I pulled the ballscrew from the SouthBend and adapted it for the Hardinge. The ballscrew is mounted on the rear of the Hardinge as well. I am using direct drive to the ballscrew using a 5 phase stepper. I have made a lot of parts with this machine. I am pretty sure that I only used existing threaded holes to mount the ballscrew. I don't like adding holes to machinery. The nut bracket bolts on where the taper attachment would have been fastened.
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Take a look at this thread for info on how to make a zero-backlash nut out of acetal for a standard lead screw.
I used these methods to make a nut for the cross slide on my Clausing 5914 and it worked really well. It would have been very hard to replace that nut with a ballscrew nut as the space is limiited, you'll seen pictures of the nut I made towards the end of the thread.
http://bbs.homeshopmachinist.net/threads/43645-Making-Acetal-leadscrew-nuts-the-easy-way?highlight=acetal
Paul T.
www.springtest.com
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Take a look at this thread for info on how to make a zero-backlash nut out of acetal for a standard lead screw.
I used these methods to make a nut for the cross slide on my Clausing 5914 and it worked really well. It would have been very hard to replace that nut with a ballscrew nut as the space is limiited, you'll seen pictures of the nut I made towards the end of the thread.
http://bbs.homeshopmachinist.net/threads/43645-Making-Acetal-leadscrew-nuts-the-easy-way?highlight=acetal
Paul T.
www.springtest.com
That's a slick way to make a zero nut. I saw this awhile back and was totally impressed. I made my cross slide out of delrin by using an Acme tap and under drilling the pilot hole a bit. X axis holds plus or minus .001" so I am happy with that. I am going to try to tap my leadscrew nut, if its still too sloppy I will get the torch out and try the old melt a thread method. Nice work and ingenuity on such a simple method.
Regarding the ball screw, I would like to see just how mr. c did his SB. Now that he mentions it I can visualize a simple way to mount it. Unfortunately by taper attachment holds my X stepper motor lol
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Thanks to all. Hood, I've had a couple of tries at buying a "Connect" CNC lathe on ebay that is ML10 based but the seller doesn't seem interested in realistic pricing. This was a conversion that was sold as a CNC training lathe competing with Denford I think. How are you protecting the leadscrew - is that a telescopic cover?
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Yes the ballscrew is protected by telesopic tubes, they were standard on the Conect lathe.
These wee lathes go for crazy prices, suppose its because you can get them in a garden shed. Mine cost me as much as my big lathe did, £300, not sure if got it for a good price or not. Probably not as it was a Yorkshireman that sold it to me and they say a Yorkshireman is just a Scotsman except the generosity has been removed ;D
Hood
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You can see them here except I dont have the end fixed in the housing I made for the thrust bearing so you dont see them extending again on the tailstock side.
http://www.youtube.com/watch?v=Kjtg5FATmAU
Hood
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Have yall thought about fixing the screw rigid and making the nut to spin? Would give you plenty of room under the Y axis plate and put the nut out the back side.
Just a thought, (;-) TP
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Presume you mean X Terry?
I thought about doing something like that as the advantage would be the motor would be fixed to the saddle but the downside was it would need a belt and pulley and a bit harder to get the bearings fitted on the nut.
Hood
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I did what Terry suggested. You may want to have a look at my Atlas conversion as I cover most of the steps.
http://www.machsupport.com/forum/index.php/topic,12484.msg80823.html#msg80823
I anchored both ends of the screw and one anchored end allows for adjusting preload of the Z. Did the same for the X axis.
Look at the pics carefully and you will see how the Z screw was adjusted from intial installation to final.
To proteact the screw i just mounted some Al angles which telescope to protect the screw. It works great.
It took a little bit more effort to make the screws adjustable but it paid off in the end. BTW, I use a torque gage to test/adjust and know just how much torque each component is using.
Have fun....
RICH
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Rich, maybe I am misunderstanding what Terry said or maybe misunderstanding the pics of your lathe but looks to me like you are spinning the screw rather than the nut.
Hood
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Hood,
Sorry, yes my screw is turning. Hmm..Eyes reading and engaged but brain not functioning yet.
To early in the morning. :D
RICH
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No probs Rich, thought I was going daft (or actually more daft if thats possible ;D )
Hood
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I was checking out some options where the ball nut spins and the screw is fixed ridgid(does not turn). Seems like other a hand full of companies there's not much out there for the DIYer. Maufacturers site lowered moment of inertia and space constriants as a few of the advantages, especially on applications with really long screws.
Robert
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Bridgeport did it that way on the X axis of the series 1 rigid rams, makes changing the belt a bit more awkward than it is on the Beaver mill.
Hood
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Well, I finally finished replacing my X-axis screw with a ballscrew. I actually used one that I bought and had machined by John Stevenson to fit an X1 mill conversion I was doing, but them I bagged a Novamill on fleabay so the X1 got unconverted and sold! The screw is a 5 mm pitch SKF, bought from Arc. The main trick was to remove the nut (usual precautions) and re-fit the other way round so the cylindrical spigot points away from the lathe saddle. (The problem here is that the original Super 7 L/S nut has a spigot 23 mm diameter that fits a bore in the saddle; with a flange to clamp on the saddle face. The SKF nuts have a 24mm spigot.) Then I machined up a simple adapter plate which screws to the face using the original 4 BA bolts, and has 4 M4 tapped holes for the the ballnut. A simple job on the CNC mill. After fitting this everything went back together easily and the performance is much improved, it seems on an initial test to take off just what you tell it to, whereas with my previous plain screw it was very hit or miss. If anyone is interested I'm happy to try to take some photos to show how I did it. I will see how I get on with just converting the X slide, as fitting a ballscrew instead of the main leadscrew looks much harder.
John.
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Pics always welcome :)
Regarding the Z, not sure if the Super 7 and ML10 have a similar set-up or not but looked to be easy enough to do on the Conect I have (ML 10)
Hood