Build Thread - BV20L 9x22 Lathe CNC Conversion

Many years ago I purchased an incomplete BV20L 9x22 lathe from eBay, (I think it is 9x22, it's hard to find specs) it was missing a few items such as the electric motor, motor pulley, chuck, various gears for thread cutting and the tailstock but apart from that all appeared to be in good condition.

The missing items besides the tailstock (which I will try to track down eventually) didn't bother me as I planned to convert it to CNC as you all know a lot of items are discarded during this process.

So this thing has been sitting in my way ever since, I’ve moved it around various parts of the garage over the years.

I've decided it is time to do something about it as it will be handy to have a CNC lathe around.

So figure I will start a build thread on it that will hopefully motivate me to start and hopefully finish it.

Thankfully over the years I have also collected a bunch of parts so I should actually have most of it to piece it together.

Anyway here are a few photos.

So I set it up on the stand today. It is just sitting there at the moment. The stand was originally designed for a smaller lathe so I will have to modify it to suit. I plan to have the lathe fully enclosed, running coolant and a chip tray on slides. I would also like to have it on caster wheels for moving around if need be and levelling feet when actually using it.

I also took a photo of the VFD and motor I will be using, well at this stage anyway.

The motor is a 1.1KW with 24mm shaft and the VFD is a 1.5KW Powtran Vector Drive VFD

The motor mount plate will need some modifications as it is a different bolt pattern.

Still need to decide what to do about the pulley setup as well. The current setup I believe uses A belts. Would a toothed belt setup be better or a combination of the two. A belt and toothed?

Not much progress but I did manage to get the new motor mount made and motor mounted. I had to make a new mount as the new motor is much larger than the older one.

I decided to mill the bracket so it fit between the head stock and the foot of the lathe.

I drilled and tapped 4 new holes in the casting as I was not happy with the ones they were done at the factory. It seems as if they just picked up a drill and randomly drilled them. They don't line up with each other!

Now I need to work on some sort of tensioner for the belt as I decided not to incorporate the tensioner in the mount like it was originally. One this is done I will temporary connect up the VFD and run the spindle.

go to the auto store and pick up at belt tensioner. They are a)cheap b)already have a spring integrated c)have sealed bearings d) easy to mount

CS900: That's a good idea, I think I will eventually go down that track, might even have a old timing belt tensioner laying around somewhere.

For the moment though I found a old and crude tensioner in my junk pile that will be enough to get the spindle running. Photos below.

Eventually need to decide what to do about the pulleys as well. Do I stay with V belts or should I go with a toothed belt or serpintine belt setup?

Would it be a good idea to use step pulleys so I am able to have a high and low range or won't this be necessary on a CNC lathe? If so what diameter pulleys should I be looking at?

I know your latest pictures show only a quick attempt at a tension system, but just for the record, any final iteration should be pushing the belt in, maximizing wrap on both sheaves and should be located on the predominant slack side of the belt. This of course would require a flat idler pulley.

Stuart

atomarc: Thank for the advice, I probably never would have thought to do it that way. I will definitely go with your suggestion.

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Originally Posted by robgeorge

CS900: That's a good idea, I think I will eventually go down that track, might even have a old timing belt tensioner laying around somewhere.

For the moment though I found a old and crude tensioner in my junk pile that will be enough to get the spindle running. Photos below.

Eventually need to decide what to do about the pulleys as well. Do I stay with V belts or should I go with a toothed belt or serpintine belt setup?

Would it be a good idea to use step pulleys so I am able to have a high and low range or won't this be necessary on a CNC lathe? If so what diameter pulleys should I be looking at?

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V belts will transmit a surprising amount of torque when tensioned properly. I don't think there is anything wrong with the belt you have there (other than atomarc comments, which i also would have overlooked!). I run a veblet on my little 8" cnc, and have never had a problem, not even with threading operations.

I do think at least 2 speed ranges is a good idea if you plan on working with a diverse range of materials. Your max speed, or high "gear", will be set by the speed rating of your chuck, but you'll probably want the extra torque of a low "gear" if you ever do larger diameter turning or harder materials.

Yeah will defiantly go with the two speed (High/Low) just need to work out what size pulleys to use.

Yesterday I wired up the VFD and had the spindle running, because that original tensioner I had on there doesn't run bearings it didn't run very well, it was was very loud and wobbled a lot.

So I decided to spend a few hours making another temporary one with a cam follower type bearing. It runs smoothly now, there is still some gearing inside the head stock that probably could come out as well to bring the noise down even more. Hopefully I did this one right.

looks great!

I'm going to ask the obvious question...whats wrong with the pulleys that are on there now?

Nothing really wrong with them. Though the way it is setup now there is only 1 speed as only 1 of the grooves on the 3 step spindle pulley lines up with the motor pulley.

That is easy enough to fix with a smaller spacer behind the pulley.

Was just thinking if there is a better alternative to V Belts I'd go that way.

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If a person hung the motor on a hinge off the back of the lathe, the weight of the motor will tension the belt automatically. Grizzly did this often on their 12" lathes. It's not hard to modify what you have now and makes it a snap, once the sheaves are aligned, to pull the belt up a tad and roll it into a different groove..all without having to fiddle around with adjustments or a tensioner...the motor weight provides the 'oink'!

Stuart

The hinged mechanism could work, though I am trying to minimise the amount of footprint the lathe takes up, maybe a ratchet/pawl style tensoner or even gear driven high/low.

I'll leave it the way it is for now as it is functional, i'd like to focus on the CNC conversion, then maybe I can get the machine to do some of the work instead of me doing it all the time. :cheers:

So before I pull this apart again to CNC, I thought it would be a good idea to do a quick test cut to ensure there wasn't any issues with spindle bearings.

I fitted a new 3 jaw chuck and had to adapt my quick change tool holder from my other lathe to the compound. I had a old bolt laying around that proved to be adequate with some minor modifications.

I was impressed with the cut quality, I was manually feeding with the hand wheels and ran the motor at 80 Hertz.

Here is some of the CNC Hardware that I may or may not use.

Still need to decide on the motors, The motor I have in the photo I was planning to use for the Z. It is a Nema23 or 24? How to I work out what size motors I need. Do I direct drive them or use some sort of reduction drive via pulleys and a belt? Assuming I will need a smaller motor for the x axis, would it still be nema 23/24?

The ball screw for the Z is 25mm in diameter, any issues with using such a large size for this? I notice some choose to also run two ball nuts, is this a good idea?

X axis ballscrew is 12mm diameter, it will be a tight fit, the ball nut might need a bit of grinding and may need to mill the cross slide a little as well. I thought it was too short initially but then I was thinking I could mount the idler bearing inside the compound instead of on the outside. If this is not a good idea, I could just buy a longer screw and mount the bearing on the outside, they are cheap enough.

Was planning to mount the X motor at the back of the cross slide, possible with some sort of reduction drive.

The drivers are M542's which should be ok.

Here are some photos