I need a parallel test bar to center workholders on my grinder and to properly level my lathe. I've been looking for one to buy but they are scarce and expensive.
I have several lathe mandrels that are duplicates. Does it make sense to grind one of these so it is concentric rather than tapered?
Should I buy a length of drill rod or drill blank stock and use that?
What do you suggest?
Gary
Printer guide rod out of a junk dot matrix printer? Shock absorber or strut shaft?
I bought a 3MT test bar from England. You're right, it was expensive. It's one of those things you'll only use once or twice. How exactly would you use one to align a lathe?
It's one of those things that you can sometimes borrow if you're in a good local metalworking club. If your area doesn't have one, then maybe you should start one.
I might be willing to part with mine AFTER I get my 9" South Bend moved to its new location in my shop - an event which may happen sometime in the next year or two.
Grant Erwin to contact me read my email address here:
If you use "Rollies Dad's Method" you don't need a parallel test bar to set up a lathe. The method may also apply to a grinder.
Pat
Greetings Gary, Instead of grinding the taper out of the mandrel just take the taper into account. When measuring using a test bar during lathe leveling the indicator must be accurate enough to measure the difference from one end of the test bar to the other to get the lathe as level as you want. This difference will be less than the taper ground into the mandrel. So if your indicator is accurate enough to level the lathe properly it will easily detect the exact amount of taper in the bar and all you need to do is put the amount of taper into your calculations. ERS
I've found it easier to use a test bar that has large diameter short length measuring sections near each end, with the middle and the very ends turned to a smaller diameter. The large sections reduce any worry about not being exactly at center height. It's not too difficult to bring the measuring sections to the same diameter (on either lathe or grinder), as you can machine each section individually without worrying about the entire length of the bar.
The test bar has centers at each end. Therefore, it's not ideal for getting the twist out of the lathe bed. But it's great for aligning the tailstock, or for aligning grinder centers.
If you use a piece of drill rod as the test bar and want to drill centers in it, you really should turn it on those centers after they are drilled. Unless you want to rotate the bar and average the indicator reading.
John Martin
Warning , this is most controversial , The 2 steamer magazines had all the Luddite machinists goin ballistic . I knew they were wrong when they said "
The book says to true a lathe head ....
Printer platten bar about 5/8" Dia , DTI on top ,near then about 8 inches away from head . Bar bend will effect accuracy .
If head is pointing up , the DTI will range different , near the head vs 8 inches away from head .
Say you rotate chuck and DTI swings
center DTI face , split the difference till the swing in one rotation is equal + and - . +6 mils then -6 mils . This is the chuck of spindle or whatever , forget it , not important now ...
Then read at 8 " .
Now without the numbers .... It dont matter if the spindle is off , only that it and the chuck be tite , no play , no slop .
A very round rod in a lathe spindle thats not gyrating too much can transfer a perfect reading of the head alignment , out to a Dial-Test-Indicator , Rod bend will void the accuracy .....
I have done a lathe spindle reading in less than 30 seconds .
Cutting a test piece to read a lathes taper is Luddite , expensive unproductive , embarrassing .... did i miss anyone ....
I love precision measure .... Im figuring cheap ways to clock stuff on a granite surface plate .
Maybe i can use a Digi-mike w/ .00005 readout to fast do transfers to my glued together 1-2-3 blocks ....
I hate using Gage blocks , for the scratching that
magically appears on their perfectly polished faces .... I wring one end , then as you slide it around , all the air gets out . If ya wring starting centered , ya leave a bit of air in the center.
Cut off the dead end of an expensive Dig-Mike and mount it as a ht gage ..... !!!
Almost as good simply using a DTI ( 0.0001 hash marks ) , but it only ranges over about .001 ! For the arc it travels .... So hand me a hack saw and a Mitutoyo ..... Any complaints ?
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