|John Rutzen||08/05/2020 13:30:27|
|348 forum posts|
I have a Harrison M250 which I have owned for about 30 years. I've never been happy with the turned finish. I've tried all sorts of tools and angles and I still don't get as good a finish as I used to with a Smart and Brown Sabel that that cast iron plain bearings and a glass hard mandrel. I've adjusted the bearings as described in the manual. I only post this because I was watching the video about Colchester lathe manufacture and it was saying how good the taper roller bearings are and how great the finish is on the part being turned. I just wonder whether others have the same issue?
8509 forum posts
Bump so this one doesn't disappear.
The M250 is on my 'better than Myford' list, and I don't think the make and model are associated with poor finish.
More likely this is a search for whatever is causing poor results. Having had my fingers burnt by poor choice of materials, blunt tools, tool height off centre, and rpm / feed rate / depth of cut, I like to eliminate them first!
As John has had the lathe 30 years, wear or maladjustment feel more likely. Before looking at the bearings, is anything else causing vibration like an elderly belt set hard, motor mount problem or something loose or misbehaving in the drive train. Bent lead-screw, worn half-nuts, loose gibs? Can the machine be turned smoothly by hand? If not can the source be isolated? After disposing of easy to fix possibilities, maybe it's the bearings.
Taper bearings are out of my league. I know long hard service can wear them out. Is that likely on this machine? I've read they have to be installed and adjusted correctly and can be damaged if not done properly, but have no idea if this is likely or not. Any taper bearing experts out there?
|Ketan Swali||08/05/2020 17:11:04|
|1417 forum posts|
As long as John can extract the TRBs, They are not a big deal to check and see what could be wrong with them.
If John googles Timken sites, there are good links on there showing pictures of bearing failure with hows and whys. I think MichaelG also put up a link a week or two ago.
If John has had issues with this machine from day one, I too think the issue may be elsewhere, but it does help to check out the bearings I guess.
Ketan at ARC.
|John Rutzen||08/05/2020 17:26:13|
|348 forum posts|
This is a machine I bought secondhand. It was made in 1985 and was a high speed version. I converted it back to the normal speed range. I was doing some cutting today in hard steel [ bits out of a printer]. The finish was poor just holding it in the chuck but a turned a section with the end supported by a fixed centre and that improved the finish. Same tool so maybe its an adjustment problem. Some people say they need to be tight, others say they can be quite slack. I always thought they needed a pre-load.
|1178 forum posts|
Have you tried seeing if you can lift the spindle ? Set a dial guage at the 12 o'clock position & arrange a lever at the 6 o'clock posistion and see if there is any play present - I would not expect to see much, if any.
I have experienced a surface finish problem on a rebuilt lathe (much larger than an M250) - chatter cutting VAM threads in an Oil Industry supplier. When checked we could get 0.05mm lift in the spindle - adjusting the bearing preload so that there was an actual preload (no lift) got rid of the chatter completely.
|Graham Meek||08/05/2020 17:46:36|
|465 forum posts|
The taper roller bearings on my Emco Maximat Super 11 have yet to be adjusted. The machine was purchased new in 1986. It has seen a lot of work, for 10 years I worked from home and this machine earned my daily bread.
According to the Emco Manual the headstock bearings are adjusted so that the spindle makes one complete turn after being pulled around smartly by hand. All gears are in neutral, as is the drive to the quadrant gears.
For my part I would be checking the slideway adjustments. All slides should be able to be moved by hand pressure alone and they should never be adjusted with any feedscrew in situ. A clock on each slide element would be how I would assess if there is any play present. Starting with the topslide and working down to the carriage to bed interface. Ensure the clock is only clocking between slideway elements. A clock for instance held in the chuck and detecting play when pressure is applied to the toolpost, can be detecting play in any one of three slideways.
The Harrison lathes I have worked on during my career have always produced good work, I hope this helps
|Pete Rimmer||08/05/2020 17:51:00|
|1219 forum posts|
I have found before on lathes with taper bearings that the inner part can be so tight on the spindle that it makes sensitive adjustment impossible. The sticktion is so much that it only moves with a pronounced 'crack' which invariably results in the user either thinking the bearing is already pulled up tight when the required pre-load has not been reached or it becomes over-adjusted due to how tight the nuts have to be to make it move.
Discounting all other checks I would pull the spindle, you'll soon know if this is the problem as it will creak loudly as you extract the spindle. If the bearing is very tight I would make an OD lap to ease the fit slightly.
|575 forum posts|
In the manual it has a section on how to adjust the bearing preload **LINK**
|294 forum posts|
Consider the Single Phase Motor may? be the problem
When you have completed all the above tasks. A similar problem with a second had lathe purchased a number of years ago I did extensive checks and adjustments. The gearbox ratlted loudly complete with chatter at most parts of the speed range. Ditched the AC Single Phase Motor notorius for running roughly. Then fitted a AC to DC Speed Control and now have quiet smooth running and cutting. So impressed fitted a variable DC motor for the power feed. Being able to adjust the feedrate on the fly for facing cuts well worth it.
6215 forum posts
Be sure and warm the lathe up then disconnect all belts and change gears etc from spindle before measuring drag as per the manual.
But worn out bearings will still play up with correct preload.
Quick and dirty check is to turn a test piece then put the fixed steady on the job right next to the chuck. And tailstock centre in place. Take another cut and if its greatly improved you probably have bearing problems.
|Michael Gilligan||09/05/2020 05:33:02|
20108 forum posts
See here : **LINK**
|140 forum posts|
I have a Harrison m250 owned for 10 years and am delighted with it I get a very good finish on most materials, gary
|Dave Wootton||09/05/2020 07:14:23|
|290 forum posts|
From experience in the past with a roundhead Colchester Student I used to have with very similar problems, I think if it is a case of adjustment Pete Rimmer has a very good point. I had tried adjusting the bearings as tight as I dared with seemingly no difference, fortunately a fellow club member had been a Cincinatti milling machine service engineer for many years, he came round and as he suspected the bearing inners were stuck on the spindle, so wouldn't adjust.
Using a large C spanner the bearing inner moved, as Pete says with a crack, and he then went on to adjust the bearings, he fitted the faceplate and adjusted by spinning by hand and checking the rotation until it stopped, I believe it was either 1 1/2 or maybe 2 turns, it was a long time ago, and it was the large faceplate.
Interestingly before doing anything else he performed the fixed steady test, using the 4 jaw independent chuck as outlined above by Hopper, also let the lathe run for a good twenty minutes before doing any checks or adjustments. He also adjusted all the slides after that the finish on the work was vastly improved, this was on a very worn machine, with a very noisy headstock ( earplugs on higher speeds!). Followed importantly with a visit to the fish and chip shop and then the pub! So very worthwhile carrying out the checks advised in the other posts , there's some good practical information in there, good luck with it.
P.S the machine was fitted with a single phase motor.
|John Rutzen||09/05/2020 08:24:44|
|348 forum posts|
I don't fancy taking the mandrel out. I can imagine gears falling out of place. Has anyone removed a mandrel on an M250? It could be the motor, it certainly vibrates. I've stuck a lump of wood onto the underside of the cabinet to stop the drumming to some extent. Oldvelo, where did you get the DC motor etc? My mill has one and it runs like a sewing machine but I think very expensive? I will try the dial gauge check and see if there is movement in the spindle. To get a good finish I've often resorted to a dead smooth file and cutting oil.
|294 forum posts|
I got the 1 hp DC motor from an online auction it came from Factory sale that had converted their variable speed drives to VFD units. The control unit is a KB Electronics AC to DC speed control KBCC “R” SCR Drive “Relay Reversing” – Chassis bought from an electronics salvage and sale company. Great for cutting theads it can be set to run forwards slowly and reverse at high speed. From memory the setup was under $250 New Zealand some 15 years ago.
A tread mill motor is an option with a few shortcomings as the top speed is around 5000 RPM and being physically smaller that an industrial motor the torque tends to fall away at less than around 1200 RPM.
An AC to DC control unit with no reverse Link to Dc Control
|Tony Pratt 1||09/05/2020 09:30:12|
|1932 forum posts|
How about some pictures of the 'bad' finish using decent sharp tools on aluminium & say silver steel for starters, I find some mild steel is nearly impossible to get a good finish even with a really decent machine?
|313 forum posts|
If you've eliminated all the possible causes mentioned by other's and still have the problem, it could well be the bearings after this time in service. High speed use and then a long 'lay up' would have a detrimental effect on the bearings.
Taper roller bearings are very easy to maintain. I would suggest you ascertain that the cones aren't 'stuck' on the shaft. If they are free you can adjust the preload to the recommended amount by the manufacturer. The bearing set must be preloaded. When adjusting, always keep the bearing moving. Forwards and backwards by hand will do. This ensures the roller moves to the correct position and seats on the thrust end of the cone.
If you have any doubt about the condition and you want to keep the machine it often pays to replace with good quality bearings such as Timken. They are not cheap though!
It probably doesn't apply in this case as your's is oil lubricated, but where the bearings are lubricated with grease, do not over fill. A common cause of failure is too much grease, it heats up and will wreck a bearing very quickly.
I hope you get get it sorted soon, it's very satisfying solving problems like this.
|Norfolk Boy||10/05/2020 08:04:28|
|66 forum posts|
Just to echo oldvelo, i have what was originaly a single phase m250, which had seen very little use by a model engineer from new. I wasn't overwhelmed by the cut finish but i was playing around wth odd tooling and materials. I did however go on to fit a 3 phase motor with vfd to Harrison spec i.e. doing away with the horrible rubber mounts and hard mounting it. The difference was remarkable not just barely noticable.
So not saying it is your problem but even when you have solved it a conversion is well worth considering.
Edited By Norfolk Boy on 10/05/2020 08:05:28
|John Rutzen||10/05/2020 08:47:19|
|348 forum posts|
Thank you for all the input. I've tried putting an 11/4 steel bar in the chuck and a dial gauge touching the top. It's impossible to get more than 0.01mm of movement so I think the bearings aren't slack. I think that's just the bar bending. I tried to take photos but they don't show the problem. It's more of a touch thing. It could be just that some mild steel doesn't cut that well. I usually stone the face of the tool and that helps a lot. I looked at the manual and taking the spindle out is a no-no. There are big circlips holding the gears in place. The motor is interesting. My machine has a 3 phase motor but I run it on single phase using a capacitor bank so I could just get a vfd unit now they are cheap from China. I got one recently and converted my drilling machine and the smooth and silent running is a revelation compared to the old 3 phase motor, never mind the speed control.
|Oily Rag||10/05/2020 16:59:57|
540 forum posts
Could be that you have inadvertantly mentioned the problem here in your last post:-
"The motor is interesting. My machine has a 3 phase motor but I run it on single phase using a capacitor bank"
The flux lead/lag on a three phase converted to single phase by use of a capacitor bank may be the real problem. I would imagine that unless the caps were tuned very accurately it would give a very interesting torque output!
To be honest it sounds like a bodge!
Invest in a VFD and I'm sure you will not be disappointed.
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