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Thread: Lathe alignment bar
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9th Jul 2015, 05:02 PM #1Most Valued Member
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Lathe alignment bar
Hi all,
With tax time coming up I'm thinking of purchasing a lathe alignment tool/bar.
I have wanted a lathe alignment bar for quite some time so this is not about lathe headstock/tailstock alignment theory but more of what size I should get. My lathe has a 5MT in the spindle, should I just get a 5MT alignment tool or should I go a size lower say a 4MT or 3MT and use a sleeve. I realise that I am multiplying potential runout but if I buy a 5MT then it's dedicated to the lathe, if I buy something smaller like a 4MT or 3MT then it may be able to be used for other "alignment" issues.
Any thoughts appreciated.
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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9th Jul 2015, 05:12 PM #2Golden Member
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I have a 5mt lathe too and also have a 3mt alignment bar from chronos in the UK. I hate the idea of using it with a sleeve....but I bought it for my old lathe so not fussed. If I had my time agaun I'd buy a 5mt one.
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9th Jul 2015, 05:23 PM #3Golden Member
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9th Jul 2015, 05:38 PM #4Cba
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The general consensus is to use a test bar that directly fits your spindle taper.
That said, it depends what you want to do with it. What sort of accuracy are you chasing? How often would you use that MT5 test bar in the next 10 Years?
If it is only occasional home use, and you have other lathes / mills that use MT4 or 3 morse tapers, you may well consider starting out with a smaller test bar. And use it on the larger lathe with a good quality sleeve. Should it turn out to be insufficiently repeatable, you could always buy the MT5 test bar later. The condition of your lathe spindle would also need be considered - if its an old iron lathe that has already seen some wear, maybe some dents in the spindle bore, you may wasting your money going for an accurate direct fit test bar. If its a pristine spindle, it is more likely you benefit from the higher accuracy of a direct fit test bar.
Chronos has some smaller test bars at a very good price, with very reasonable postage. Like this MT3 for $93 including shipping:
http://www.ebay.com.au/itm/3MT-LATHE...-/371176267409
I have been looking at this for a while.... then again, for using it maybe twice a year, is it really a necessity? As long as the basic lathe alignments are fine and undisturbed, I think not. For me, I rather spend the money on tools. Also, keep in mind that real test bars are hollow inside to reduce weight and the unavoidable sag. I do not think that these cheapies from China are hollow, it would surprise me if they were.
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9th Jul 2015, 06:57 PM #5Senior Member
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For what's it worth I'm no expert.
I bought a MT3 bar for my lathe (mt5 headstock) from the LPR toolmakers. I align between centres using a sleeve MT5-3 in headstock with a dead centre in head and tail stock.
Repeatability within 0.02mm(dial indicator run along the bar setup on centre) However I think its a little hypothetical when you start turning depending on all other factors including machine rigidity involved in turning something concentric
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9th Jul 2015, 07:50 PM #6Most Valued Member
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Thanks for the replies. Well the MT bore in the lathe is pretty good. It hardly gets used. The reason for the test bar is to allow me to align the headstock to the bed. I few years ago I totally stripped the headstock and replaced the spindle bearings. This involved the total removal of the headstock. When I replaced the headstock I did re-align the headstock to within what I considered to be "reasonable" tollerances. (The headstock has two adjustment bolts on one side, typical of most Chinese lathes) However, I did it when all I had was a starrett 98 level. Being a little green I also sat the level over the V ways. Now I know better and I also have a more sensitive level but it now means that my headstock alignment is not as good as I initially thought. It turns a taper of about 0.03mm per 100mm, not an issue for most of my work but a little annoying for some things. I have been able to reduce this further by twisting the bed but I would rather fix the problem and have the bed straight. I also wouldn't mind a test bar for an easy way to align the TS when required. Cheers, Simon
Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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9th Jul 2015, 08:16 PM #7
Recently someone posted that they bought a test bar direct from Aliexpress or similar and I remember thinking it was quite cheap. If you can find the thread you maybe able to get one of each for the usual cost of one.
…..Live a Quiet Life & Work with your Hands
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9th Jul 2015, 08:25 PM #8Philomath in training
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Of course, if you had a method of cylindrical grinding there's this option -
Test bar.pdf
Michael
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9th Jul 2015, 08:38 PM #9Cba
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That is about the one and only lathe adjustment that really, absolutely, requires the use of a test bar as in practice it cannot be done without. But only once. Once that headstock is aligned, there should be no need anymore for that test bar. I do not assume you ever want to remove that headstock again. Any chance you could borrow a test bar?
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9th Jul 2015, 08:42 PM #10Most Valued Member
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Michael, when you've finished your grinder, I'll order a M2 X 12", for you to test it out on, if that's OK.
Kryn
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9th Jul 2015, 09:16 PM #11Golden Member
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I have had these test bars on my watch list for a while.. no intention to buy as I already have MT3 & MT5 bars.. $80 shipped is pretty good (note no MT5): http://www.ebay.com.au/itm/400931434788
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9th Jul 2015, 09:41 PM #12Most Valued Member
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Hi Chris, I hate borrowing tools. If it were hundreds of dollars then borrowing would be more attractive. No I never want to remove the HS again. Probably shouldn't have done it last time but I did! Michael, cylindrical grinding I'm getting close to achieving (well if you can call it that) but I would also need to make a TTA for it to be smicko. If I were to buy an undersized alignment tool, would a 3mt alignment tool in a 3mt to 5mt sleeve be any less accurate than a 4m alignment tool in a 4mt to 5mt sleeve? A 3mt alignment bar could be used in many other applications... Simon
Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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9th Jul 2015, 10:13 PM #13Philomath in training
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The 'if' here is the relative accuracy, but an interface is an interface - if the parts are within the same accuracy limits it will not change the result.
A test bar is something that I find I use probably once every couple of months and not to line up my headstock. I use it centre to centre to line up my tailstock horizontally and on the dividing head to check the angle is horizontal if I've moved it. They can also be used to check the alignment of the tailstock taper and the alignment of drill press sockets. All sorts of uses.
Michael
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9th Jul 2015, 10:16 PM #14Golden Member
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9th Jul 2015, 10:30 PM #15Golden Member
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