Test bar

B

BenW

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Hello. I recently-ish ordered a mt2 test bar, along with some other stuff. Unfortunately the test bar went out of stock before my order was packed. The company offers another test bar that is a combination mt2/mt3, and I told them they could send me that one instead. I had considered that one when I originally ordered but it is really long and slender, here is a picture:

52069cad33975de1b843bdfc2944ba48.jpg


so I thought I could just chop it in 2 and have 2 separate bars of more appropriate length. I decided to go with the other one at the time, but now I ended up with that bar anyways. Does anyone see any reason I shouldn't cut it in 2? I would lose the centreholes but I guess I could make new ones, or just make my own bar for indicating between centres. The test bar is 450mm/1.5 foot long FYI, and the cylindrical portion is 300mm/1 foot.

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When using the MT2 end of the double end test bar in the spindle for a head stock alignment check, the MT3 end will be too heavy, and will cause droop in the bar, especially with that length. Cutting it in half would likely be OK for only using either end with just the MT end in the spindle. Putting new centers in the cut ends that are accurate enough with the existing O.D. for using as a test bar is not trivial to do correctly.
 
Bob Korves said:
When using the MT2 end of the double end test bar in the spindle for a head stock alignment check, the MT3 end will be too heavy, and will cause droop in the bar, especially with that length. Cutting it in half would likely be OK for only using either end with just the MT end in the spindle. Putting new centers in the cut ends that are accurate enough with the existing O.D. for using as a test bar is not trivial to do correctly.
Click to expand...
What is the best way to check and align the tail stock is what I am going for.
 
You don't need the tapered end to check tailstock alignment. A test bar running between centers at the tailstock and headstock will do the job. https://www.edgetechnologyproducts.com/tailstock-alignment-bar/ The tailstock offset is adjusted until indicator readings are the same at each end.

It is possible to do the adjustment with a modification of the Rollie's Dad's Method where the the test bar is mounted between centers and a lathe dog is used to drive the bar. The spindle is rotated and when the averages of maximum and minimum readings is equal at either end, your tailstock is aligned. The only requisite is that the bar be round and of equal diameter at either end and of equal diameter, easily verified with a micrometer. The centers need not be perfectly positioned for this to work.
 
Looks like that was intended to align an MT2 tailstock with an MT3 headstock (or the other way round). Too long to just stick the MT2 or MT3 end in a spindle and leave the other unsupported.
 
A two collar bar held between centers is the best way to check and align the tail stock. You can make an accurate one yourself, even if your tail stock is not in alignment. Like this one:
293270
I made my own out of DOM tubing and steel end plugs which were machined from bar stock and pressed in, then the assembly made accurate. It seems counter intuitive, but a highly accurate test bar can be made quickly and easily on a lathe that does not have the tailstock in alignment, and can then be used to set the alignment properly. I can explain how if you are interested, but it is a bit long winded if nobody is interested in making one.
 
It does indeed seem awfully long and slender, especially with the weight of the mt3 end hanging in the air. I used rollies dad's method to align my headstock (reasonably well anyways) and I might use that to align the tailstock too. As you say it isn't critical that the centre is precisely located, tough it is helpful. Nevertheless, I'll hold off on cutting the bar until I need it, which is whenever I feel like having go at aligning the headstock even better, and maybe scraping the tailstock a bit to take out the nod.

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Bob Korves said:
A two collar bar held between centers is the best way to check and align the tail stock. You can make an accurate one yourself, even if your tail stock is not in alignment. Like this one:
View attachment 293270
I made my own out of DOM tubing and steel end plugs which were machined from bar stock and pressed in, then the assembly made accurate. It seems counter intuitive, but a highly accurate test bar can be made quickly and easily on a lathe that does not have the tailstock in alignment, and can then be used to set the alignment properly. I can explain how if you are interested, but it is a bit long winded if nobody is interested in making one.
Click to expand...
I made a similar makeshift bar from a piece of steel stock and used it to align the headstock, I'll probably have a go at making one with lapped collars and a stiff, lightweight tube(carbon fibre?), eventually.

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i use the edge test bar shown in bob korves thread. got my south bend to less than .001 in all directions at both ends
 
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