Rivett 1020s VFD Conversion Motor Size

[alcro1998]

I recently picked up a pretty nice 1020s.

Ways seem to be in great shape and only some minor issues with it.

The big thing is there is no reeves drive in the machine at all. The motor is just coupled to the belt system with a long shaft and some lovejoys.

I guess the previous owner that used it only needed 3 speeds???

The guy I bought it from never used it but got it from a guy who had it since the early 70s.

Pretty much I’m going to do a VFD conversion on it and was wondering the suggested motor size? I have a nice Baldor 7.5hp inverter rated motor but not sure if it’ll be too much power or if it’ll even fit in the machine properly.

Any suggestions are greatly appreciated.

Thanks,

Chris

 

[beckerkumm]

I assume both back gears are still working and those are your three speeds. As stout as a Rivett is, a 7.5 hp should not be overkill and your new Baldor has probably got a smaller frame than the original 5 hp. I'm not a Rivett guy but I can't see why that size motor would not be appropriate. Dave

 

[alcro1998]

I assume both back gears are still working and those are your three speeds. As stout as a Rivett is, a 7.5 hp should not be overkill and your new Baldor has probably got a smaller frame than the original 5 hp. I'm not a Rivett guy but I can't see why that size motor would not be appropriate. Dave

Thank you Dave. 7.5hp seemed about right to me. The only VFD conversion I could find the guy used a 5hp motor which seemed small to me unless there were fitment issues with a larger motor.

Both back gears work on it which are the 3 speeds I was referring to.

 

[beckerkumm]

I think the low gear is something close to a 10-1 reduction so 5 hp is likely enough but it comes down to how slow you want to go in the direct drive gear. some prefer to use as much range as possible in the higher gear so the larger motor is a benefit- as is a vector duty motor that operates better at the extremes. As heavy as a Rivett is, it is not a hog machine so with the back gears, 5 hp has good torque. Assuming a 1800 rpm motor, a 7.5 will be a 213-215 frame vs 182-184 for 5 hp. On my CVA it was the P head location that caused issues but the motor shared space with the 6 speed gearbox. Dave

 

[alcro1998]

Back at the shop again today.

Looks like the Baldor 7.5hp motor might just barley fit. The motor is massive for a 7.5hp motor. Even the couple 10hp marathon electric black max motors I have are smaller.

I’ll try and fit the 7.5hp motor but if it won’t work I’ll just get a different 5hp motor. Don’t need to go too overkill especially since the Rivett has adequate back gear reductions.

 

[beckerkumm]

Interesting. My Baldor IDNM 5 hp is a tad smaller than a similar Black Max. I attributed that to the frame being cast iron on the Baldor and Aluminum on the Max. The 7.5 and 10 hp should be the same frame size. Dave

 

[tailstock4]

I believe I would go with a 7.5 hp or maybe a 10 hp. If you wanted to have similar performance to a 10EE, the 7.5 hp would probably work assuming both have a 1-to-1 belt drive. If you wanted it to be closer to the original Rivett drive, I believe it would probably take every bit of 10 hp with a VFD.

I don’t think the two back gears are going to help you much past 400 rpm. The mechanical advantage of the Reeves drive and 5 hp is pretty significant in the lower rpm ranges as compared to a VFD. The Rivett is a more powerful machine than the 10EE. In my shop it occupies a space between a Monarch 10EE and my Pratt & Whitney 12c gearhead – meaning it has attributes of both although not as smooth or convenient as the 10EE but also not quite as powerful as a gearhead.

I believe the Rivett is a really good candidate for a VFD and will even help address a couple of its shortcomings such as a quicker speed adjustment and better control over braking and restarts of the motor although it will still have a lack of a brake and significant spindle coasting at higher rpm’s when the clutch is returned to neutral but the motor is left running. I’m working on adding a brake to address this on my machine.

 

[beckerkumm]

Is there enough benefit to trying to keep the 4000 rpm top end with a vfd conversion? Living with a 3000 rpm top end would give full hp up to 90 hz or close to 2500 rpm and top out the 3000 at < 120hz.. I do see the benefit of the larger motor with 12.5-1 and 6.25-1 back gears now. Dave

 

[Mr_CNC_guy]

If you are using the full HP at 3000 RPM those chips are really going to be flying, and they will be white-hot! Not my idea of fun.

 

[rke[pler]

Small diameter stuff likes high speed, so if that's in your bailiwick I'd keep the speed.

 

[alcro1998]

I will be keeping the top speed. My machine is an older 3500rpm machine.

The current drive motor is coupled to where the reeves drive output would be. Not sure what the direct drive ratio is on the machine but the Baldor motor and ME Black Max motor I have both are rated for high speeds so should be able to hit 3500 rpm no problem.

The 7.5hp Baldor I have is a 254TC framed motor. That should give me 1/4” of height play on the motor shaft if my tape measure estimates are correct.

Since I have the 10hp Black max though I’ll probably just end up using that. It seems like the Rivett is more than capable of handling 10hp and I probably won’t even come close to using the entire 10hp.

I have done a couple VFD conversions in the past so hopefully everything goes smooth. Really nice being able to pull the whole drive out on these and not working on the ground.

Picture of it since no post is complete without it. Also so happy to have a cam lock one.

 

[beckerkumm]

If you are keeping the top end, the Max is a good choice. I'm putting the same motor in my 60/61 although the speed range isn't needed for it. Torque and hp fall off over 90 hz but at high speeds you aren't usually needing or wanting it. While the Rivett can handle 10 hp, the size tooling generally used may not but a sensible operator knows the limits.

Keep us up to date on the conversion. sweet machine. Dave

 

[Halcohead]

You might want to check page 17 of this PDF (page 5 of the promotional literature for the 1020S) : http://vintagemachinery.org/pubs/2379/4491.pdf . Your 10hp motor will be plenty. Note the original Reeves drive had plenty of power drop-off, just like a VFD, and only put 1.5hp at the spindle at 400rpm running open belt. This chart is what I used to size the motors for my lathe.

When I did a VFD conversion on my 1030F I used 5.5kW (~7.4hp), 1800rpm motors (https://dealerselectric.com/00418ET3EAL112M.asp also, wow the price on these has gone up >50% since 2017), driven by a 5hp TECO A510 VFD. The 5.5kW 1800rpm motors are 1.6hp at 400rpm, so a little better than the original Reeves drive. In retrospect I should've run the 7.5hp VFD, oops. Luckily the 7.5hp VFD has the same packaging as the 5hp VFD, so should be an easy drop-in replacement someday.

The 5hp VFD is ample; I have startups tuned to be quick, and adding a braking resistor allows the lathe to stop in a second or two, as well. With heavy cuts or largeish drills (>3/4"), the speed will slow a bit, especially when running in open belt. In the lowest back gear I've never noticed problems with the motor bogging, but maybe I just haven't pushed things hard enough. I've never stalled the motor or errored the VFD in a cut.

My VFD started to error out above ~3400rpm with the motors I chose, so that's my redline. So far I haven't missed the higher RPMs, and I do plenty of 5C work. Heck, an HLVH only goes to 3000rpm.

The biggest annoyance is the lathe has to be warmed up for 20-30min when running in a cold shop (<55degF or so) before it can be reliably started in open-belt. When the oil and bearings are cold the VFD struggles to get up to speed. Largely the warmup hasn't been an issue though; I just start my work in backgear or if I know I'm going to run the machine I start it as soon as I get to the shop. A larger VFD would surely reduce or eliminate this behavior (and allow even more aggressive startup/stops).

Some more conversion details in case they're useful to you:

I believe the metric-frame motors were the only option that fit through the cabinet door because they allowed me to put the wire box in the specific orientations required.

I used two separate, identical motors, one to drive the backgears and one to drive the open belt, and used the original FWD/REV contactor in the cabinet to switch the single VFD between the two motors (since you have to stop the spindle to switch between back gear and open belt anyways, this arrangement works fine). The contactor is controlled by a microswitch under the cover at the left end of the headstock that senses the position of the backgear selector knob. This way you just have to change the one gearbox lever to go between backgear and open belt, rather than the two selections the original drive required. (I also did this because the original back gear/open belt clutch assembly had problems on my lathe, so using this with a single VFD-driven motor would've been annoying).

The hardest part of the conversion (since I'm not an electrical engineer) was getting the original tach to work (I was willing to make big changes under the hood, but the only external change I wanted was replacing the speed control buttons with a potentiometer). The tach is 0-28V, but the VFD outputs 0-10V analog for speed. I had to make a small op-amp circuit to multiply the VFD speed signal by 2.8 to get the tach to work.

All the other functions of the lathe (spindle stop due to threading, etc) were straightforward to wire into the VFD and preserve functionality with.

Oh yeah I added a bicycle disc brake with 160mm rotor to the backgear motor pulley to allow me to lock the spindle when changing chucks (since my machine is L-0). The brake is necessary; even with the lathe in its lowest backgear you need the brake active to loosen/tighten the spindle nut. You can probably get away without the brake since your machine is camlock. Someday I'll integrate the brake control into a foot pedal on the lathe (with microswitch to turn off the motor of course), but that's a low-priority project.

If for some reason you want the original Reeves drive, I still have the motor and hardware removed from my lathe. I'm sure we could make a deal.

That was a lot of words but I hope some of them were useful.

 

[beckerkumm]

Very interesting and informative. Do you have pictures of the two motor set up and why you went that route? Also, was there a problem with the Reeves ? I know they can be finicky and hard to work on but they are also an ideal way to get variable speed. The later Smart Brown, Schaublin, and even Moore used similar methods. Dave

 

[alcro1998]

Thanks Halcohead.

I think I might just stick with the 7.5hp motor then since it looks like it matches original performance. I don’t really use high speeds ever right now but I like having all original functionality.

I’m tempted by the original drive but looks like you’re in California and I’m in Ohio. I think my motor is original and even if it’s not I don’t think I’d want the original motor.

I’m planning on getting a Chinese 7.5kw drive regardless of the motor size I use. I have had good experiences with the Lapond drives and know my way around them a bit.

My machine has a spindle lock but someone did the classic engage it while the spindle is running and it’s pretty screwed up. Luckily my headstock isn’t cracked as that seems to be an issue. I’m going to try and remove it but not sure if it’s possible without taking the whole headstock apart.

2 motor setup sounds very interesting to me as well. Pics would be appreciated

 

[Halcohead]

Alcro, it sounds like you're in good shape. I think you're making the right choice skipping my drive hardware; even if it was nearby and in perfect condition, who knows if it would even fit the 1020S base anyways (mine is an "F" series, and they definitely made changes to the drives over the years). Looking at the photo of your lathe, someone has removed all the original control switches under the headstock. You might want to look in the electrical cabinet to see what wiring/hardware is left there, since a lot of it can be reused for the VFD retrofit.

Very interesting and informative. Do you have pictures of the two motor set up and why you went that route? Also, was there a problem with the Reeves ? I know they can be finicky and hard to work on but they are also an ideal way to get variable speed. The later Smart Brown, Schaublin, and even Moore used similar methods. Dave

Thanks! I'll snap some photos tomorrow or Friday when I'm at my shop. Disclaimer: My shop and work is not the museum-caliber of many members here.

I can't say my reasoning was necessarily watertight, but a few things drove me to do a VFD conversion:
- Softer starts (& stops). At high speed the original drive pulled serious current, which is fine in my current industrial space (just upsized the breaker), but won't be fine in my future shop spaces.
- Original drive had lots of vibration which I wasn't looking forward to tracking down. Of course I've since found out other parts of the lathe need balancing anyways.
- Wanted speed control with a simple turn-of-a-knob (a-la a 10ee), rather than waiting for "faster/slower" buttons, a-la an HLVH (or my Nebel Microturn, for that matter).
- Original drive was pretty worn (the backgear/open belt clutch was having problems that were hard to diagnose, & the motor brake had long ago worn out).
- I never liked having to switch two levers to go between backgear & open belt (it's not as bad as a South Bend, but come on that is an absurd comparison).
- I don't like all the dust Reeves drives shed.
- Lastly, possibly to the chagrin of collectors out there, this lathe is a platform for learning/practicing engineering & machining for me. This was the most-involved drive design/industrial controls project I had done up to that point, and was a good learning experience for that.

 

[beckerkumm]

All fair points. Vibration kind of defeats the purpose of that quality of build. Great thing about the high end stuff is you have something to work with when making the effort. How precise does Rivett still turn? Dave

 

[alcro1998]

The electrical cabinet on the end had the covers and push buttons. Also the motor brake in pieces and the small reeves drive motor and gears.

Not too useful on the conversion. I might reuse the push button covers but I don’t think I’ll occupy all the spaces after the conversion.

Attached is a pic of the current motor setup. Really don’t know why anyone would do this to a Rivett.

 

[tailstock4]

In reference to the publication http://vintagemachinery.org/pubs/2379/4491.pdf that was referenced earlier. I could be wrong but when I look at this chart I see the power loss at the spindle of about 1.5 hp at 400 and 3,600 rpm. I find it unlikely that a 5 hp Reeves drive would lose 3.5 hp at 400 rpm at the spindle. I also think that when considering motor size for a VFD conversion, that the Rivett at 400 rpm with the Reeves drive on my machine has about a 4.5 to 1 reduction. This gives a pretty significant increase in torque and should be factored in.

In my shop my Rivett sits next to my 10EE which has a VFD conversion with 7.5 hp Black Max close loop motor with a 1 to 1 pulley ratio with back gear. I believe that at 400 rpm these machines are similar in power when in open belt – although I’ve never stalled the 10EE. My Rivett has a turret attachment which allows some pretty aggressive feeding of large drill bits and I know that with a 6” steel chuck fully tightened on 1 ¼” stock, the drive had a enough torque to spin the stock in the chuck and not come close to stalling the drive. If I were going to do a VFD conversion on the Rivett and if given the choice I would keep the clutch as there are some advantages to having a clutched headstock and the option of slow manual engagement.

One note regarding cold weather operations... I noticed on the Rivett when I worked on the spindle and headstock is that I think because Rivett uses gear trains for both threading and especially feeding that at high speed there is a bit of noise and gear vibration. I believe this explains in part why Rivett chose to use an ISO 150 oil to help dampen the effect of gear noise. Because of this heavy oil the Rivett spindle bearings seem to be fairly sensitive to the amount of oil they receive. It is possible to get too much but in cold weather this heavy oil can take an extended period of time to reach the bearings. Something to be aware of in a cold shop.

Also even at moderate speeds with a clear plexiglass cover on the headstock I notice quite a bit of oil wraparound on the gearing and spindle. I estimate almost a third of the oil is drawn up. For these reasons I decided to switch to a synthetic oil. I use Mobil SHC 629 which is an ISO 150 oil which helps maintain the gear dampening effects but flows much faster, is less temperature sensitive, has some friction reduction properties and comes off the spindle and gearing quicker. This oil is more expensive but because there is no clutch, pump or brake in the headstock, there’s little contamination and with a clean headstock it should have long life and change interval.

 

[beckerkumm]

This is interesting and I need to understand the difference between torque and hp supplied through a variable pulley vs a vfd. I know the vfd can provide whatever torque the motor is rated for, until it is overspeeded, usually above 80-90 hz. HP is reduced as speed is decreased in a constant torque setting. I know I can't slow my 5 hp vector ( 1000-1 ) motor down by hand at any hz above 1. What I don't know is how different the relationship is with the Reeves or how much power the Reeves itself sucks up. I think some of the mechanical advantage of the Reeves is negated by its consumption but don't know or understand the details.

I have a clutch on both my S and B 1024 and CVA and agree that they are worth keeping, even with a vfd. Dave