Unimat3 vs. Sherline lathes

[david bennett 8Participant @davidbennett8]

Dave, my scooter motor i rated at 120 watt. It is a brushed pm motor. Naturally, being Chinese , I suspect that is the wattage going in, and less coming out. Its more than the original, but not by too much.

dave8

[david bennett 8Participant @davidbennett8]

double post

dave8

[david bennett 8Participant @davidbennett8]

ps -my drive belt is 4mm diameter green fusible.

dave8

[Graham MeekParticipant @grahammeek88282]

[david bennett 8Participant @davidbennett8]

Gray, the carbide boring bar I used was sharp, but the low doc. was almost certainly caused by an over- large radius. I take your points, but don’t forget that I am looking into why the Sherline e.g appears to perform better. This has led to an examination of the spring washers (the only substantial difference) Why were they used? No other maker that I know of uses them. A simple extra thread on the spindle would have allowed the conventional system to be applied. It seems to me that a large pressure on the spindle may overcome some of the springiness of the washers and let the spindle thrust vary, causing chatter. An increase in the thrust on the front bearing may not be matched by an increase on the rear bearing, as the rear bearing is relatively free to move in the headstock.

dave8

[JasonBModerator @jasonb]

If it were an insert bar rather than solid then at a minimum you would want an insert designed for the difficult metal alloys, better still a CBN insert to stand a half decent chance with a bearing that could be upto 62 Rockwell

Trying to cut with a lesser general purpose insert even if new will not really work, even a **GT will struggle.

As Gray says grinding would be another option.

[david bennett 8Participant @davidbennett8]

Luckily, when I tried this and achieved a cut, I didn’t know it was impossible!

dave8

[Michael GilliganParticipant @michaelgilligan61133]

[SillyOldDufferModerator @sillyoldduffer]

[david bennett 8Participant @davidbennett8]

S.O.D., no chance of a side-by-side lathe comparisom. I have never even seen a Sherline in real life. I think the motor and controller are ok. – it did achieve the cut. As you say, the only way is to replace the washers, but that would mean permanently altering the original spindle. Before doing that, I thought I would ask here for comments. I don’t think my lathe has any meaningful faults.

dave8

 

[Graham MeekParticipant @grahammeek88282]

[david bennett 8Participant @davidbennett8]

Graham I was not using an insert cutter. It was a solid carbide bar ,sharp on the cutting edge and with a large nose radius ( this was to go in an 8mm hole)

As for belleville washers presenting a constant force on the bearings I think that is open to question for reasons already given ( the rear bearing outer shell is relatively free to move within the headstock)

dave8

[david bennett 8Participant @davidbennett8]

I have just had a thought that I would like to add. Consider the Unimal db/sl. It ight be simpler to modify this sprung spindle to the more conventional style. After all, the watchmakers spindle does not use belleville washers.  If it proves to be advantageous it would add to the evidence.

dave8

[Graham MeekParticipant @grahammeek88282]

[John HaineParticipant @johnhaine32865]

I have a U3 and have looked at Sherlines at exhibitions and IMHO the Sherline is far better made.  The Unimat just doesn’t have a nice precision feel.  I bought the U3 before I fitted a 3ph motor and inverter to my S7 for small diameter high speed turning, but having upgraded the S7 I never use the unimat.  One day I’ll pop it back on eBay…

[david bennett 8Participant @davidbennett8]

John, thanks for your comments on the Sherline. That is a surprise. They don’t look too well made in photos.(I am using the u3 more as I get less mobile – at least it is small, light, and versatile, as I imagine the Sherline to be )

dave8

[david bennett 8Participant @davidbennett8]

I recently bought a Chinese solid state luggage scale. I used it to measure the compression on a u3 spring washer stack and got a figure of about 13 lbs. So this is the constant preload on the u3, and considered good for the bearing life. If a constant preload of 13 lbs. was applied to the sherline spindle, it would be considered too high, and bad for the bearings. Who is right?

dave8

[SillyOldDufferModerator @sillyoldduffer]

[Michael GilliganParticipant @michaelgilligan61133]

Perhaps … just perhaps … this might inform the discussion:

https://glockcnc.com/sherline-spindle-headstock-upgrades/

I saw this page a while ago, and have at last found it again.

”Get thee behind me Satan”

MichaelG.

[Graham MeekParticipant @grahammeek88282]

The loading of 13 lb supplied has confirmed my initial thoughts that the Spring Pack has not been assembled correctly.

My Spring pack easily exceeds 28 lb and is assembled as Emco intended. To compress this spring pack when I re-assembled the 8 spring washers used. I needed two pieces of M6 studding in the motor mounting bracket holes, a U shaped bridging piece to allow access to the circlip and two M6 nuts to wind down the bridging piece.

At 13 lb I could have easily pushed the assembly together with my bare hands.

I am all for comparing like with like but there needs to be a level playing field with machines in as manufactured condition. There is also the difference in the length of the cross-slides of the two lathes to factor in.

Regards

Gray,

[david bennett 8Participant @davidbennett8]

Gray, that makes the comparable sherline even more over-preloaded.

dave8

[Graham MeekParticipant @grahammeek88282]

I have just set-up a Dummy Spring pack from the spare washers that I have available. The Spring pack in the free state is 6 mm overall height.

Under a static load of 14 lb this overall height was reduced to 5 mm. Thus the Spring pack has a rate of 14lb/mm.

If memory serves me correctly there was more than 1 mm of movement before I could get the circlip into the groove.

Thus my 28 lb is in the right ball park if this movement was, as I suspect 2 mm. If this movement was only 1.5 mm then it would still be 21 lb.

Therefore to move the spindle against the Spring pack initial preload would need a loading greater than either of these figures.

Regards

Gray,

 

[david bennett 8Participant @davidbennett8]

Gray, I can accept that. I was guarding against the stack bottoming out and giving a false reading. I am confident the pack is assembled correctly.

[HollowpointParticipant @hollowpoint]

[Michael GilliganParticipant @michaelgilligan61133]

My third attempt at posting this

Another Glock link:

https://www.youtube.com/watch?v=8SKFKwAs_f0

 

About 9 minutes of explanation about their bearing options.

MichaelG.

[Author]

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