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Harrison L5 Alignment Question

Hi All, having got my L5, and re-motored etc it so i can now use it I came to the question of alignment. It is not on the usual harrison cabinet, but rather a big box leg under the headstock, and a A leg under the tailstock end. It was a training lathe, an early mk3 from the serial number and looks of it (from lathes.co.uk :) speeds 22-480rpm on the plate. I have turned a test piece on it, but im not sure how to interpret it... help please:

the test bar was 3/4" dot matrix printer carrage guide ( lying around...) chucked 2.5" in the 3 jaw, with 4" sticking out. turned a dumbell shape as follows: a light skim to clean up, then 1/2" from the real end to

3/4" from the chuck waisted by about 50 thou. touched up the tool and then took a 5 thou (indicated on the cross slice dial) cut fron one end to the other, which obviously didnt cut the middle bit. When measured with my mike the end away from the chuck is 2.5thou smaller in diameter, in 4". Firstly should I worry about this? ( i think i should) secondly is my test piece 'solid' enough? I only have a 1" mike, so cannot really go much bigger, the 'ends' are 1/2" long, is this to much?. lastly which way do i shim the tailstock? none of my setup books tell you, they just say "as appropriate" :( I think its the rear leg?

thanks

Dave

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small.planes
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In article , small. planes writes

2.5 thou. diameter (i.e. 1.25 thou deviation) in 4 inches? I think I would too. IIRC, 10% of that figure would be in the acceptable range, but I haven't time to find a source.

Well, if you think about it, if workpiece deflection was causing the difference you would expect the tailstock end to be *larger*. Perhaps running the tool several times at the final setting would be useful, but I doubt if it is a significant issue here.

If the tailstock end is small it means the saddle is too close to the centre line at that end. Thus you are right, the rear tailstock foot (if there is a foot) needs shimming.

David

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David Littlewood

Thanks,

Ill try shimming tonight. It does have 'feet' so at least that easyish. any ideas on how much would be needed? Given the hugh size of the bed is there likely to be any other cause? turned the bar all over first, which should eliminate headstoc alignment i think? The tool might not be exactly on center, it face off with the tinyest of pips, could that make such a difference?

sorry for all the questions, but this is my first time...

Dav

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Well, some complicated geometry and you could work it out, but life's too short. I would try shimming it 5 thou a time or so and see how it went. You probably need to be quite consistent in how tight you bolt down the feet though, a torque wrench might help.

Sorry I can't help more, I have several books on machine setting up and reconditioning, but I'm rushing to get ready for a trip.

The effect of the tool being off-centre is often cited as important when turning tapers, but I think this has been much exaggerated; I saw a good calculation recently which suggests even tens of thou has only a minor effect. For cylindrical turning I don't think having the tool a little low will affect this issue - the pip on facing may be the worst problem it causes. Having the tool high is to be avoided as it can make for the tool digging in if it deflects.

However, making a simple tool height gauge may usefully be one of the first things to make for your lathe. A 1" cylinder, careful faced ends (see below) with a similar cylinder bolted to its top, offset, with the break at exact centre height, and you can set tools in a few seconds whether they are right way up or upside down rear mounted ones.

The pip is a nuisance but easily removed with a graver. More important to check your lathe does not face the end convex. Dead flat to very slightly concave would be fine, otherwise everything you face will not seat properly on a flat surface and will be a bane forever.

David

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David Littlewood

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Well, some complicated geometry and you could work it out, but life's too short. I would try shimming it 5 thou a time or so and see how it went. You probably need to be quite consistent in how tight you bolt down the feet though, a torque wrench might help.

Sorry I can't help more, I have several books on machine setting u and reconditioning, but I'm rushing to get ready for a trip.

Ive set it up ok now, took 48 thou in the end. went up in a couple o steps, to small, went to far, then came back. :) turns less than 1/ thou large at the free end in 5" on 1/2" diameter, I can believe tha might be flex in the bar, one of my books has upto 3 thou in a foot a acceptable. Ill let it settle for a bit and use it then check again.

The effect of the tool being off-centre is often cited as importan when turning tapers, but I think this has been much exaggerated; I saw good calculation recently which suggests even tens of thou has only minor effect. For cylindrical turning I don't think having the tool little low will affect this issue - the pip on facing may be the wors problem it causes. Having the tool high is to be avoided as it can make fo the tool digging in if it deflects.

I guess Im over paranoid.... Ill settle down once Ive made a few thing on it ;)

However, making a simple tool height gauge may usefully be one o the first things to make for your lathe. A 1" cylinder, careful face ends (see below) with a similar cylinder bolted to its top, offset, wit the break at exact centre height, and you can set tools in a few second

whether they are right way up or upside down rear mounted ones.

a nice simple job to start with :) With the power feeds and things need some so i can get used to it. Its much scaryer than my littl super adept or unimat.

The pip is a nuisance but easily removed with a graver. Mor important to check your lathe does not face the end convex. Dead flat to very slightly concave would be fine, otherwise everything you face wil not seat properly on a flat surface and will be a bane forever.

Facing was the next thing i was going to check, but Ive got to get th gasaxe out to cut a piece to face, so a job for the weekend.

Thanks for you help

Dav

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