Lathe sine bar

[Susquatch]

Its metric, 50mm centers

Here is one at Little Machine Shop with 2.5" spacing that would work with standard 5" sine plate gauge blocks. It isn't even hinged like yours. It's only the bar.

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littlemachineshop.com

Note that the stated precision is in the same order as my tailstock barrel. "Working face parallel to bottom of rolls within 0.0002", center distance of rolls accurate to 0.0003". So ya, best not to get too anal about it.

 

[Aliva]

I don't understand this one Aliva. I was suggesting that the pins contact the tailstock, not the plate, nor 4 pins.

If the compound is too close, I suppose one could use a standard parralel bar to do the same thing.

Sometimes I am my own worst enemy. The goal is to make your simple plate even easier to use by eliminating the need to use an indicator. If we make it too complicated, we have defeated that objective.

But still, it's a worthy goal. Great ideas often build on other good ideas.



And here I was wondering if mine was a problem! So you have answered the question. 2 thou is 2.5 minutes. Big deal.

Mine is 3 tenths over 2.5 inches or 0.4 minutes. I can't imagine that being much of an issue for most tapers. I think it is important to remember that there are lots of sources of error in such systems. It's prolly not wise to be too anal about it.

I think you still have to have the 2

pins contact the compound and tail stock with the same pin

 

[PeterT]

Here is one at Little Machine Shop with 2.5" spacing that would work with standard 5" sine plate gauge blocks. It isn't even hinged like yours. It's only the bar.

Yes I saw that one. Sine bars seem happiest resting on gage stack vertically like on a surface plate or table, but less fun orientated on their side in a lathe angle setup. Trying to make surface contact & adjusting the compound & not let blocks slip into the chip tray needs more hands than I have. A lockable one can be preset up on the surface plate & transferred over to the machine.

 

[Susquatch]

I think you still have to have the 2View attachment 34560 pins contact the compound and tail stock with the same pin

Yes, that is exactly what I pictured.

@PeterT - picture setting the gauge blocks on the top instead of the bottom. Wouldn't be hard to do until the stack gets too big.

 

[John Conroy]

Here's my version, made up of a chunk of 1/2" thick hot rolled plate, two 1.5" long 10mm dowel pins, and nine 8mm X 3mm magnets. The pins on mine are spaced on 5" centers and I have printed a "Table of Constants for a 5" Sine Bar" from the Hermann Schmidt Company (easily found with a google search and a very nice pdf chart) for quick reference.



Try to ignore the gouge made during a bandsaw mishap, the operator has been chastised repeatedly!



Here you can see it set to give a compound angle of 29 degrees, 30 minutes. The table of constants says for that angle and a 5" sine bar, the constant is 2.462" so I have stacked under one of the pins a 2" plus a .350" plus a .112" gage block. The magnets are strong enough to hold everything in place while I sweep across the face with an indicator and adjust the compound angle until the indicator needle is stationary.





I have a cheap 83 piece gage block set and have measured every piece and they are all accurate to within .0002" so plenty good enough for me.

The engraved numbers on the compound of my lathe are off by about 1 degree and a few years ago when I got the lathe I put 2 small center punch marks on the compound and the space between them is where the line should be. I sure wish I hadn't done that now.

 

[Aliva]

Tangent engineering has an other product to set an angle using the tail stock offset method for cutting long tapers.
It consists of a steel block with a 90' V along it's length. You clamp the block to the stock you want to taper, with the supplied clamps, attach the compound sine bar to the block with the appropriate gauge blocks for the angle you desire, use an indicator adjust the tail stock till you read zero on the indicator. Dudley Tool Wright demonstrates it's set up. scroll to 7.32 in the video. Dudley also uses a tapered center drill to drill the stock to allow for the tail stock off set.