Unimat3 vs. Sherline lathes

[david bennett 8Participant @davidbennett8]

I was looking into why the Sherline appears to perform better than the u3. The only substantial difference seems to be the spindle thrust arrangement. It would have been simple and cheaper for the u3 to gave used double locknuts (as on the Sherline) rather than the belleville washer arrangement.  Are there any benefits from the u3 arrangement?

dave8

[HollowpointParticipant @hollowpoint]

No benefits I don’t think. I imagine it was done like that to keep costs down.

[Graham MeekParticipant @grahammeek88282]

There are several benefits for using Belleville Washers. Yes one is a cost element, but another is the fact that the bearings get a constant loading and therefore will have a longer life span. This would not be the case with a manual adjustment. This loading would have been advised by the bearing supplier. Based on the size of the machine and the expected usage.

The larger Compact 5 uses a similar bearing arrangement. This arrangement is also self compensating for any temperature variation. This would be critical with the low wattage motor driving the U3 & 4 lathe. Power from the motor being used to overcome tight bearings. Instead of productive work.

From experience bearings are regularly overtightened in the pursuit of backlash or play elimination.

Most of my engineering career I have had Emco equipment, with some Myford’s thrown in for good measure. The bearings of those Emco machines although sometimes un-orthodox have never once let me down. Either in their longevity or in the items produced using such arrangements.

Regards

Gray,

 

 

[david bennett 8Participant @davidbennett8]

I am a great supporter.of the u3, but I wonder why the Sherline, an apparently poorer-built lathe can seem to out-perform it. There are several videos online showing the Sherline taking depths of cut which would just cause unbearable chatter on the u3.  I wonder if the Belleville arrangement allows the tool pressure to shift all the bearing pre-load to one side allowing the rear bearing to float and chatter. I realise too great a cut could exceed the recommended practice, but the bearings are so simple to replace that I regard them almost as consumables. ( I have a more poweful motor on my u3 )

[JasonBModerator @jasonb]

Have you a link to these videos. Depth of cut is only half the equasion, you also need to condider feed rate.

Neither of these machines are really meant for taking heavy cuts but in the right hands can both produce good work which is probably the better overall indicator of performance not just DOC

[Michael GilliganParticipant @michaelgilligan61133]

Sherline’s own videos are reasonably impressive:

https://www.sherline.com/sherline-videos/test-cuts/

One man’s deep cut is, of course, another man’s light scratch.

MichaelG.

[david bennett 8Participant @davidbennett8]

Graham, wouldn’t your Compact5 struggle to match some of Michaels references?

dave8

[david bennett 8]

On david bennett 8 Said:

Graham, wouldn’t your Compact5 struggle to match some of Michaels references?

dave8

Sorry I thought the question was relating to spindle bearings. As regards metal removal rates I am not getting into that debate.

My Compact 5 and Unimat 3 do all the things I ask of them, in a time frame I find acceptable. Metal removal rates was something I was prepared to compromise on when I downsized my workshop.

As regards the Sherline I cannot say I am a fan. There are elements of the design which are good, but others like no quill on the milling machine I find un-acceptable for my style of working.

Regards

Gray,

 

[Graham MeekParticipant @grahammeek88282]

For those who like to do comparisons, here is the Compact 5 Chart taken from the C5 Handbook.

 

 

Regards

Gray,

[JasonBModerator @jasonb]

Well I dusted mine off and although I would not have taken the same DOC as the Sherline link shows when I used the U3 in the past but for the sake of comparison gave it a go.

16mm 230M07pb. 540rpm which is the nearest to 500rpm on the sherline. First 0.75mm DOC then 2.5mm DOC. (These are depths on the Sherline site) Original EMCO 6mm HSS bit (same one that allows 6.35mm DOC on my warco280) Cut Dry. Standard motor. I just quickly eyeballed ctr height so that may be a bit off.

The only time I got chatter which is easily heard was when changing my hand position as I could not use two hands to get a steady feed due to holding the phone to take the video. The perished belts slipped on the 2.5mm cut otherwise I could probably have fed a bit faster. Auto feed belt bu**ered

To me that is very good “performance” from such a small light hobby mill and if you are expecting more from that then you have got the wrong machine or attitude towards using it

 

[bernard towersParticipant @bernardtowers37738]

Im with Jason a lot depends on feedrate, I regularly turn 6mm leaded !a to 1mm in one pass with my Taig the feedrate is slow but the finish is excellent and on dimension.Sharp tools are the answer!!!

[david bennett 8Participant @davidbennett8]

I feel in danger of being misunderstood. I am not praising the Sherline, or downing the u3. I am trying to find out if the u3 might benefit from a modification to it’s thrust/preload. This is the real question.

[JasonBModerator @jasonb]

Did my video answer your question?

You seem to think that Gray’s C5 will not cope with some of the cuts shown on the Sherline site so I assume you also find your own U3 chatters with these size cuts. Which ones are you getting chatter with?

I don’t have the need to machine Titanium, Inconel or the shanks of milling cutters so can’t comment on those but as my video shows the U3 was quite capable of doing the same cuts in mild steel as the Sherline so I’d tend to say there is not much point in modifying it.

I should add that my machine is quite worn as I did not know better at the time when I got it and often used the Emco grinding wheel on it with crumbly white wheel going everwhere and also used Dremel cut off discs in it. The HSS but had no fancy honing, I just gave it a quick lick with the belt sander before doing the video, think I have an 80g belt on it at the moment.

[david bennett 8Participant @davidbennett8]

I recently had to cut a ball race bearing inner for a clearance fit.It was 8mm i.d. Using a carbide boring bar worked, but at only at about 0.002″ doc. I got the feeling that a less resilient thrust arrangement might help. The Sherline arrangement came to mind, with it’s positively clamped locknuts

dave8

 

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[Graham MeekParticipant @grahammeek88282]

For several years I worked a new Hardinge HLV Toolroom lathe. The party piece at the Machine Tool Exhibitions for this machine was to machine 1″ diameter EN1A Pb down to 1/16″ diameter. The headstock bearings of this lathe were assembled in a temperature controlled environment. This lathe also benefits from a variable electric feed, which can be balanced to the cut.

At the time I was working this lathe the U3 had just been introduced and I purchased one of the first into the UK. There was actually a waiting list for these lathes. I could have purchased 450 U3’s for the cost of the Hardinge, just to get things into perspective. Yet I was impressed by the finish such a cheap machine could produce and it was a great improvement over the SL.

If I need 1/16″ bar I usually buy this in.

 

Regards

Gray,

[david bennett 8]

On david bennett 8 Said:

I feel in danger of being misunderstood. I am not praising the Sherline, or downing the u3. I am trying to find out if the u3 might benefit from a modification to it’s thrust/preload. This is the real question.

Or maybe not!

Apart from the bearing design, are the two machines in similar condition?   A U3 will be at least 34 years old, unlikely to be in ‘as new’ condition, and possibly badly worn – everything a bit loose.   In contrast, a much more recent Sherline is likely to be in good order throughout.  Condition matters!

The motors are different too.

It’s hard to guess what the U3 designer was trying to achieve.  Maybe he was compromising on cost by specifying a cheaper bearing and a washer.  Or the spring washer could be an overload warning, allowing chatter whenever the operator takes a cut likely to overstress the motor or drive train.   Or it’s a mistake!

Likewise, we don’t know what the Sherline is optimised for either.   Could be they are optimised for good cutting performance when new, but aren’t expected to last more than a decade or two, if driven hard.

I think the only way to find out is to increase the pre-load.  Unfortunately, excessive preload causes rapid bearing wear…

Dave

[david bennett 8Participant @davidbennett8]

Dave, I wasn’t intending to increase the preload,just to lock it more positively within it’s parameters. I take your point on wear,but I have upgraded the motor. With fairly recent bearings and slides locked where possible, it should comparable. I am surprised that the u3 system is considered cheaper. Instead of the washers, it would only have needed an extra thread and 2 locknuts on the spindle to get positive endplay, instead of possible movement caused by flexible washers

dave8.

[Graham MeekParticipant @grahammeek88282]

By way of a comparison, the U3 was set up with an Arc Euro 6mm square Knife tool. (Not ideal for large metal removal rates).

At 550 RPM the max cut on a 19mm diameter bar was 2.5 mm deep, 5 mm off the diameter. With a 12.7 mm bar a max cut of 3 mm was possible, 6 mm off the diameter. By adjusting the PWM control I could get to a 3.5 mm cut.

As this machine was overhauled by me recently I would consider it to be in as new condition. (There is a post somewhere covering the overhaul). The limiting factor with this machine is the O-ring belt drive. Not due to slippage, but due to the elasticity of the belt itself. This elasticity can set up an oscillation in the drive as the tension in the belt fluctuates. Keeping the tool pressure constant is of key importance. That does not mean I am dissatisfied with the drive system nor am I likely to change it.

The Compact 5 was tried using the same tool. The 19 mm bar at 330 RPM would easily cope with a 4 mm cut, 8 mm off the diameter. This could be increased to 4.5 mm if I used some cutting oil.

At 550 RPM and by way of imitating the Hardinge demonstration. The 12.7 mm bar was reduced to 0.7 diameter in one cut of 6 mm depth.

This machine was new in the late 1980’s. It also has a proper Vee Belt drive and a more powerful Induction motor. Yet the dimensions across the bedways of each machine are the same. What is different is in the design of the cross-slide. Which is about 3 times the length of the U3 and thus has more bearing area, which yields greater rigidity.

EN1A Pb was used throughout.

Like I said earlier these machines do all I ask and metal removal rates do not prove anything. If anything I tend to use the CNC approach, a lot of quick power fed cuts of around 1 mm deep. Timing the use of a tipped tool using this approach it was found to be considerably quicker than one large cut powered by me, by a couple of minutes.

Those of you who have been following the C5 modifications will know I recently added a refinement to the cross slide dial. The bearing adjustment was carried out during the winter months, (7-10 C workshop ambient temperature). When I went to use the lathe yesterday the effort to turn the cross-slide handwheel was not as I remembered it. Slackening the adjustment and resetting restored the correct feel. Workshop ambient was 26 C yesterday.

Regards

Gray.

(Grammar error)

[david bennett 8Participant @davidbennett8]

Perhaps I should have mentioned that my u3 is powered by a variable drive scooter motor and has vee pullies and round fusible belts. I have no complaints re. metal removal rates in mild steel.

 

 

 

 

 

dave8

[david bennett 8Participant @davidbennett8]

Thanks for all the comments. I offer my conclusions in case it help anyone. I shall not be changing the thrust adjustment on the u3. There seem to be 2 different reasons for chatter. First is chatter when there is no cutting pressure (well illlustrated in JasonB’s video when he changes hands) I think this is a result of the necessary bearing clearance, so unavoidable. The belleville washers may be emco’s attempt at a cure. (this also occurs on lathes with more positve thrust locking e.g. Pultras) Second is when under a heavy cut. I think this is where the whole lathe is “flexing” and acting like a spring, so also unavoidable.

dave8

[Graham MeekParticipant @grahammeek88282]

Just by way of a little experiment. A hook was held in the 3 Jaw Chuck of my Unimat. The hook was threaded and a nut behind the jaws would stop this being pulled through the chuck jaws. A 0.002 mm per division clock was arranged such that the probe located on the ground face of a chuck jaw.

Using a spring balance loads were applied to the hook towards the Tailstock end of the lathe. This would apply an additional loading to the Disc Spring pack. Movement would only occur when the the load applied was greater than that exerted by the Disc spring pack.

The Spring balance topped out at 28 lb with no movement. While I could have multiplied the spring balance loading with a suitable lever. I thought better of it, as I cannot see any tool applying a loading greater than this, especially in this direction.

Regards

Gray,

 

 

[david bennett 8Participant @davidbennett8]

Impressive, Graham. I was trying to reproduce this experiment, but couldn’t find my spring balance. It struck me that it is difficult to estimate tool pressure when applied through a screw thread. Can I ask you to apply your spring balance to the toolpost and stress it to 28lb in the direction of the tailstock. Then how much effort is needed to overcome the presssure with the feed handle?  (when cutting the bearing it took considerable pressure)

dave8

[Graham MeekParticipant @grahammeek88282]

Sorry that is not something I am prepared to do with my machine.

The above test was a pure pull on the bearing pack.

Putting a large offset load on the toolpost is not the same thing as when the tool is cutting under normal conditions. Much of the load from the tool is taken downwards. With some deflection towards the operator during normal turning. Or away from the operator when boring. This deflection puts a twisting moment on the toolpost / carriage assembly.

Increase the loading on the tool and this will increase the downward load and the twisting moment.

Regards

Gray,

[david bennett 8Participant @davidbennett8]

OK, I was simply wondering if 28 lbs is a reasonable estimate. I have just ordered an electronic luggage scale and will measure it myselif.

 

 

Thanks anyway.

dave8

[david bennett 8]

On david bennett 8 Said:

Perhaps I should have mentioned that my u3 is powered by a variable drive scooter motor and has vee pullies and round fusible belts. …

 

 

dave8

The motor and drive train are important because they decide how power and torque are available at the  cutter.   In principle, putting a more powerful motor on a machine will enable it to remove more metal faster, but overdoing it may not work out that way.   Belts slip, bearings wear, the carriage lifts, the tool-post twists, the cutter bends, and so do the head and ways.  Small lathes aren’t particularly strong or rigid.

How powerful is the scooter motor?  The U3’s designer deliberately specified a rather small motor: probably proportioned to match the rest of the machine and improve precision and longevity.  Maybe the scooter motor has taken the U3 out of it’s comfort zone, so counter-intuitively it doesn’t compare well with a factory Sherline?

Dave

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