Taper Tantrum

[G-ManBart]

The scale on the taper attachment is an indicator not a measurement.
Just finished cutting a Jacobs taper on the Hardinge, the indicator was close.
I use a test bar between centres, with a dial indicator on the tool post and a dial indicator on the bed or the DRO
In your case zero both indicators, move the carriage 1.15 inches and the tool post should move .030, half the taper.
Adjust the taper attachment until you get that.
Make certain the indicators are parallel to the movement or you'll get sine errors large enough to affect the measurements.

Greg

Not to argue, but why would they list the lines on the taper as inches per foot and degrees if they aren't supposed to be a measurement to get you close?

I don't expect them to be really accurate, but to set it at 1.5* and get 1.1* seems a bit much...that's off by 30% or so.

As I said in the first post, I can make the part using indicators to set the taper, I'm just trying to figure out why the scale is so far off.

 

[twhite]

Ok just a thought. Correct me if I am wrong. The taper attachment only connects on the ways on one end? It that is the case could the bar be bent some? You could check as suggested by mounting indicators. Set at an angle on the scales. Measure movement. Then reverse the angle and measure. If there is a noticeable difference the bar may be bent.


Cutting oil is my blood.

 

[ErichKeane]

Silly question: Did you make sure the taper attachment gib was tight, and that the backlash was out of it? I find on mine that the first ~1/4" ends up not tapering very much as the backlash runs out. BUT at that point its a bit obvious as the 'taper isn't straight.

 

[jaek]

Maybe the scales are off by 0.4 degrees instead of by 30%. You can use an indicator to set the attachment for 0 degrees and see what the scales say. Could be slop in the pivot point or something.

 

[G-ManBart]

Thanks to everyone who's given me ideas...pretty sure I (we) solved the mystery.

First thing I did was confirm everything was tight and/or adjusted properly, etc....no changes there.

I then put an indicator on the compound and set a carriage stop (no DRO....yet) so the carriage could travel exactly 6". I backed well past the starting point to remove any backlash and then advanced the carriage from the starting point. The compound moved exactly .150" in 6" of travel, so .300" per foot which would be a .600" per foot taper since it would be taking .300 off per side. This works out to 1.432* using the online calculators. I had it set on 1.5*, so I think that's within reason for a crude scale.

This got me thinking, so I went back to the original part and, eureka! saw the problem. I must not have been paying attention carefully enough, but there is a flat section with no taper right near the top! I don't know how I missed that, but will blame it on being sick the past four days. I ignored that section and measured from the small diameter to where the taper stops, used the new length and got 1.4* and change (didn't write it down since it was a crude measurement on the part). All along I was thinking the scale should put me within maybe a tenth of a degree, and it seems a bit better than that. At least I don't have to fix anything but the wiring between my ears!

Short version...it was all me, and the taper attachment seems to be fine. Thanks for everyone weighing in and helping!

Bart

 

[twhite]

Thanks to everyone who's given me ideas...pretty sure I solved the mystery.

First thing I did was confirm everything was tight and/or adjusted properly, etc....no changes there.

I then put an indicator on the compound and set a carriage stop (no DRO....yet) so the carriage could travel exactly 6". I backed well past the starting point to remove any backlash and then advanced the carriage from the starting point. The compound moved exactly .150" in 6" of travel, so .300" per foot which would be a .600" per foot taper since it would be taking .300 off per side. This works out to 1.432* using the online calculators. I had it set on 1.5*, so I think that's within reason for a crude scale.

This got me thinking, so I went back to the original part and, eureka! saw the problem. I must not have been paying attention carefully enough, but there is a flat section with no taper right near the top! I don't know how I missed that, but will blame it on being sick the past four days. I ignored that section and measured from the small diameter to where the taper stops, used the new length and got 1.4* and change (didn't write it down since it was a crude measurement on the part). All along I was thinking the scale should put me within maybe a tenth of a degree, and it seems a bit better than that. At least I don't have to fix anything but the wiring between my ears!

Short version...it was all me, and the taper attachment seems to be fine. Thanks for everyone weighing in and helping!

Bart

Glad you got it all sorted out.


Cutting oil is my blood.