View Full Version : Lathe to grinder conversion?

Ragarsed Raglan
10-12-2002, 11:57 AM
I've just been given a load of bits and pieces for my Raglan lathe from an old friend. In amongst the bits was the majority of a training lathe that Raglan manufactured for schools use; it's called the Loughborough (pronounced 'Luff~boro') and is a 10" swing x 12" BC. It has been used with a capstan attachment, and never having a saddle or cross slide assembly, in its former life, the bed is unmarked from a wear viewpoint. In amongst the spares I was given I got a saddle assembly and a tailstock from the 'full size' Little John model - these will fit the Loughborough bedway.

What I have in mind is to resurrect this machine into a cylindrical grinder, by using my toolpost grinder mounted permanently on the saddle/cross slide and with the spare tailstock. The reason for this is the head spindle is flat belt driven (internal under drive system) with only 3 speeds. I figure the flat belt will give a better finish when used for grinding. I aim to protect the bedways with some convoluted protectors. The machine never had any system for racking a saddle along the bed - but this can be a system copied from its 'big brother'. The tailstock fits straight on with no problems. I figure I can then use tooling (like chucks, collets, and live centres and driver centers) off the 'biggun'.

My grinding requirements would fit in the lathes envelope nicely.

My question is - has any one done a similarly dedicated conversion to a lathe before? and what comments would they make about this project?? All other comments gratefully recieved.


John Stevenson
10-12-2002, 12:37 PM
Couple or three things I can think off.
First off I was faced with the same thing a while ago when I stopped using a C7 Myford Capstan. I was going to swap the bed over with my everyday ML7 so I had a new bed but I finished up selling both to make room for a larger machine.
The Loughboro has taper roller bearings in the spindle. Whilst these are more than adequate for a lathe you may find swapping over to a conical bronze bearing and sleeve will give a better workhead finish.
Finish will also be affected by the rigidity of the toolpost grinding head but this could be beefed up. Possibly the biggest archilles heel could be the size and rigidity of the cross slide.
It could also pay to change the cross slide screw for something a bit finer as 10 tpi is a bit course for a grinder.
I have a Myford MG 9 grinder and these use a 20 TPI vee thread type screw with a large weight hanging off the back to remove backlash.
Hope this may help.

John S.

Ragarsed Raglan
10-12-2002, 02:22 PM
John S,

Thanks for the reply - that's just the sort of comment(s) I was looking for.

Since posting the question I had considered a ME 40 tpi thread for the cross slide to give a 0.050" on diameter per rev infeed ~ and if I was doing this I think I would adopt a 'split nut' aproach (as Colchester) to remove backlash. Albeit not as a constant anti backlash system as you describe.

I accept the point about the T/P grinder rigidity (one ofthe reasons for dedicating the Loughboro is it would be more of a permanent feature and could be worked up acordingly). What I hadn't thought about was the taper roller headstock (do you know if these are the same P5 grade Timkens as the LJ?). I suppose the way to go would be an air bearing! but I'd need a grinder to do that!! I must admit to being a bit ignorant of grinder designs - are taper rollers 'verboten' for a grinder?

The size of the Loughboro is just right (fills the last little gap in the workshop I was worried would stay empty!). Also it came with its base stand, and I've just found the coolant system so can keep the dust down a little.

I'm so excited by the project I've even cancelled a 'Curry & Pub night out' to start on it - Mrs. Raglan is not pleased!!


John Stevenson
10-12-2002, 04:02 PM
The 40 tpi could be a bit fine especially where grinding dust is kicking around. Most grinders tend to have big ~5" to 6" handwheels to get decent numbers around the edge.
As regards taper bearings in the spindle could be alright for this job. Go for it first and change if needed. Not may grinders run bearings on the spindles, they prefer bushes.
When I was an apprentice many moons ago I used to run a big Churchill crank grinder doing the crank shafts on RR Merlin engines. These used a 30" diameter wheel to get inside the webs. We lifted these on with an over head crane and you could see the slop in the spindles as they let go. They used to have about an 1/8" of up and down!!
We just used to start these up and let them get to speed and get some oil round. After about 3/4 of a hour and the spindle was 'floating' on a film of oil you could start using them. Any quicker and you had small flats all over the crank.
Once warmed up you never switched these off and left them running all day.

I also used to have a cam grinder which started life as a capstan lathe. Built by Glynn Jones, Myfords development engineer during the war. This was basically just what you propose but with a sub rocking bed and all plain bearings. If you locked the head up you could do plain grinding with it and the finish was very good.

Just thought of something else.
You need to split the tailstock from it's base and have a quick screw adjustment to alter the alignment. In theory the alignment shouldn't alter but it does. You grind one piece and dial the tailstock in. Change the work for a longer piece and you have to do it all again. Rememebr we are talking tenths of thou's here. Most commercial grinders have the bed pivoted in the centre and you swivel it to keep parallel. Similar the the universal bed on a milling machine.

John S.

PS. Probably a bad night for the curry anyway.

PPS> Don't know if you know it but I used to work at Raglan Engineering making the Aprons and screw cutting gearboxes just prior to their closure by Myfords.

[This message has been edited by John Stevenson (edited 10-12-2002).]

Ragarsed Raglan
10-14-2002, 08:52 AM
John S,

I'd guessed you were one and the same John Stevenson that had written the piece about Raglan Engineering on Tony Griffith's excellent website!

First off, I stripped the spindle out and it has got P3 Timkens. They look like the original fitment! I'm inclined to go with these, as the finish I get with the Little John when using the toolpost grinder is pretty good (much improved when I converted to 3 phase motor and a VFD ~ the manual variable speed control system has been retained and by running at a combination of juggled manual speed / electronic set speed I can achieve good results; probably due to removing hetrodyning from the system) I'll keep in mind the plain bushes though.

I take on board your comments w.r.t.the 40 tpi feedscrew. My aim is to be able to grind motorcycle crank pins to 0.0002" overall tolerance (these are built up cranks for a single cylinder), and I was considering a M&W type inspection micrometer head with tenth vernier reading. Maybe the larger size is the right way to go.

I once had a half share in a Brown & Sharpe cam grinder that came out of the Triumph Motorcycle works at Meriden. This used a rocking table with the master cam at 1:1 ratio, to size of the finished production cam ~ whereas the method of producing a master cam was done at a 10:1 ratio, a neat solution. The follower riding on the master cam was a radius that was changed as the wheel was dressed to a smaller diameter, there were about 20 different followers to select from dependent upon wheel diameter and engine constraints (i.e. whether the cam being ground was for use with a flat or radius follower) I would like to consider a similar cam grinding attachment for this project; only here I would need to have the wheelhead rocking ~ and that throws up thoughts about scrapping the idea of using the T/P grinder and going with a dedicated design.

I wondered about mounting the wheelhead on a slow taper adjustable table similar to a Clarkson 6" X 12" sub table complete with rack system, but on retrospect I like the idea of setting over the tailstock.

Thanks again John for your comments ~ I'll keep you informed as to the progress (or otherwise!!)