Reference bar ?

[NigeParticipant @nige81730]

Does anybody make a round bar that has a morse taper on one end and say 10 inches of bar left that is known to be concentric, straight etc. If so what is it called please? I have tried searches using terms like "lathe reference bar" or Headstock reference but not getting anywhere.

[NigeParticipant @nige81730]

[not done it yetParticipant @notdoneityet]

Change reference for test. They are not cheap.

[Phil super7Participant @philsuper7]

Try RDG Tools or Chronos they both sell test bars

[NigeParticipant @nige81730]

Thank you guys, using 'test' was the key, finding what I was looking for now 😀

Nige

[RobboParticipant @robbo]

Nige, see your messages

[PeteParticipant @pete41194]

If your wanting to use that test bar to check your lathes headstock alignment and I think you are, then there's a way around buying one if you've got a large faceplate for the lathe. Clean, adjust the lathes cross slide, nut and gib so everything is as it should be. Take a very fine clean up cut across the full width of that faceplate. Remove the compound slide, back the cross slide out towards you, set up a dial indicators tip just past the faceplates center at the 3 o'clock position and the magnetic indicators stand on the cross slide. Run the indicator away from you with the cross slide towards the backside of the faceplate. Your measurement changes between the center of the faceplate and it's outside edge will be DOUBLE what any misalignment is. On a good toolroom lathe in new condition the cross slide is biased inwards and machined, ground, and/or scraped so the lathe should face concave .001"-.003" over 12". IF? and it's fairly rare your headstock is out of alignment the above test should show that. With smaller lathes using a 10ths reading DTI for the measurements might be better than a .001" reading dial indicator. There's far too many on forums and Youtube avocating adjusting the headstocks alignment without properly testing that it is in fact the real problem and not something else. A very well made test bar can indicate problems, but the headstocks internal Morse Taper has to be spotless, in perfect concentricity and condition or it will show a misalignment that the headstock doesn't have.

If your wanting to check the tailstock then assumeing it's MT is concentric and in very good unmarked condition a test bar can help. But I'd start by extending it's quill fully out, locking the quill clamp, then run an indicator along the top and then along the side that's closest to you. The tailstocks bed clamp should also be used during that test. These tests will show more than using just a test bar will and especialy so if your Morse tapers aren't perfect. I do have some of those expensive test bars and I still do the above tests first. A seriously worn tailstocks base and spindle bore can show misalignments that have to be addressed first before any meaningful tests can be done.

Edited By Pete on 10/07/2017 00:51:12

[John McNamaraParticipant @johnmcnamara74883]

Hi Nige

You do not have to have a perfectly aligned test bar, it will help a lot if you have a good piece of ground bar the same diameter throughout its length. 250 to maybe 300mm is fine overall length allowing for 50mm in the chuck.

First put the bar in the 3 jaw or better still the 4 jaw and center it the best you can with an indicator.
Then mount an indicator on the tool post nicely centered on middle of the the bar.

Then maybe with a felt tipped pen mark the bed every say 1cm. for the length of your test bar.

Finally rotate the spindle until you find the low point and the high point and note the readings on a sheet of paper

Do this for every mark.

Buy subtracting the high from the low point You will get a reading of the mean….
Stick to one convention Always low from high or high from low, don't calculate some of each. some numbers may be minus. You will be writing down thous or tenths plus or minus creating your graph line 

The result will not be the same for every position unless the spindle is perfectly aligned to the bed
If you graph the results you will get either a straight line if the error is constant or it may be curved if the bed wear is uneven.

Hope this makes sense, Its easy to do and is not affected by any error in the spindle nose taper. You are measuring the true axis of rotation.

Regards
John.

I posted this a while back,

On testing the cross slide alignment assuming that (first) the the spindle is correctly aligned to the bed. The cross slide and saddle can get out of square due to wear.

It will help if you put a (tested straight) bar in the four jaw chuck, then firmly but no more tighten the bar in the chuck. It is very important not to over tighten and distort the bar.

Then rotate the chuck and bar testing against an indicator mounted on the cross slide or the lathe bed touching near the end of the bar, If the indicator measurement is not the same when the bar is rotated end for end lightly tap the bar until both ends have the same indication.

Once this is done you know that the face of the bar is at 90 degrees to the axis of the machine, and you have eliminated any error that may have been introduced by the chuck or face plate.

Then once set rotate the bar until it is horizontal, and move the cross slide with an indicator fitted touching the bar it in and out You be able to see any errors at any point along the bar.

It is accepted (By some) that if there is an error it should make the lathe face slightly concave. maybe .0002" over a foot but never convex.

Cheers
John

Edited By John McNamara on 10/07/2017 06:58:50

[NigeParticipant @nige81730]

John, again thank you. At first read I think it makes sense but I will have to go over it all a couple of times with the lathe and a bar in front of me to get the techniques and the thinking to sink in 😀👍

Nige

[simondavies3Participant @simondavies3]

A couple of words of warning – depending on your source of bar, test the test bar first. I purchased one from an Indian source and discovered some curious readings.

Once I set the bar between the end centres it became obvious that:

• the taper and the bar were not aligned
• the bar was not circular but a sort of oval shape

further checking revealed that it is a MT2.25 taper – or something like that – it is too fat at the large end so doesn't even fit tightly into the headstock…

Mr eBay was kind enough to refund my money with no quibbling once it was established that the seller was no longer a member of eBay.

I have purchased a replacement (also from India) and it has tested out successfully.

If anyone can suggest a use for a ground bar, roughly circular and to that well known size of (roughly 18.35mm), attached to a (roughly) MT2 taper, I would be pleased to hear them…

BTW, please don't assault me with "should have bought from X and not India, China, etc", I bought it with my eyes fully open and am not complaining

Simon

[Antony PriceParticipant @antonyprice56876]

Hi Nige

Do a search in Youtube on

"lathe headstock alignment"

"lathe tailstock alignment"

for some visual demonstrations on the techniques for checking alignment

Tony

[Howard LewisParticipant @howardlewis46836]

Nige,

Have sent you a PM

Howard

[VicParticipant @vic]

Perhaps this may be of help Nige.

**LINK**

[Author]

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