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Retromilling
6th Oct 2008, 07:32 PM
It took me a while to work out how this taper attachment works but eventually I figured it out.
I got the basic idea from an American guy but he did not have any real idea of how a sinebar function worked so I had to work out what was needed to calculate the required collar thickness ( Sinebar stack height) myself, that was the hard part.
The gauge sits on top off the compound rest and the two lower extensions of the vertical shafts keep it inline with the compound slide. An extra lengthways bar can be added as can be seen in the diagram if you have a external dovetail compound slide.
It is held in place by a thread and lock plate to stay rigid on the compound slide. Heavy clamping is not required.
Then you loosen the compound slide so it can turn freely.
Then you extend the tailstock shaft so both vertical shafts can push against tailstock shaft (lock tailstock) . It can also be sett against a precision bar placed in the chuck or between centers.
The vertical shaft at one end can have an accurate machined collar that is machined to a specific sinebar stack height (thickness ) , that slides onto one vertical shaft as in the photo and diagram .
If you move the cross slide until both vertical shafts touch the tailstock shaft with the compound unlocked , then the compound slide will be forced around to a specific angle as controlled by the thickness of the accurate machined collar placed between one vertical shaft and the tailstock shaft.
Or it will sett the compound to parallel with no collar attached.
Outside surface of compound slide has to run true to the dovetail , mine is very close.
The setting collar should be a quite loose fit on the shaft so it's real thickness is applied between the gauges shaft and tailstock shaft .
Also the vertical shaft closest to the tailstock should touch the tailstock shaft first before the shaft that is closest to the center of the compound so it can have leverage against the center position of the compound slide. Otherwise the compound will not move.
It is important when making the gauge that the two shaft holes be drilled nice and parallel in both plains. However the actual distance apart is not that important except that it must be measured and the exact roll distance recorded.

To calculate the roll distance , when the gage is finished and the shafts are locked tight , measure the outside distance of the two shafts then subtract the diameter of one shaft.
This distance will vary slightly with temperature changes.

I have attached two DOS based computer programs that will calculate the thickness of the collar , block or feeler gage required ( sinebar stack height ) to produce a certain taper.
The precision protractor is very good for milling machine but this is better and quicker for the lathe for short tapers if you don’t have other options.
Once you have made a specific collar for a certain taper , you just drop it on the shaft and line the compound up and away you go .
Also tapers can be sett with a gage block of specific thickness held in place by hand or even thin feeler gages for very slight tapers.

The two DOS based programs are zip files , they have been scanned for any virus and I have been using them with no major problem .
They will unzip with WinZip. Unzip the files of each program into its own folder. Then click on EXE file. Sometimes the MS DOS shortcut will not work or the program terminates before calculating .
Open properties of shortcut and open Programs tab . Uncheck box that says " close on exit " this will stop it terminating . If the shortcut does not work just use the exe file to open not the shortcut.

First you use taper .zip files , EXE file to open program to calculate the half angle of any taper.
You enter : -- Small end diameter. : --- Large end diameter. and Taper length.
Or you can enter Large end, length and taper per inch. I generally use taper per inch as I feel it gives more accurate results.
This is any standard specifications for a taper.
This then shows a whole lot of information about that taper including half angle in degrees.

Then taking the half angle you open the " sinebar stack height " program .
Enter distance between rolls ( center distance between two vertical shafts on compound attachment ) in inch. ( say 4 inch) Can be any distance as long as you know it very accurately.
Enter : --- D for decimal degrees .
Enter : -- The half angle from the first program in decimal degrees.
This will read out the stack height which is the thickness that you need to machine a collar to set the compound to the correct angle of the taper specifications that you first entered.
Nearly went crazy trying to work out the details but it is fairly simple once you make the attachment and play around with the programs.
It is a sinebar function turned on its side and applied to the angle between the compound slide and the center of the lathe ( tailstock shaft)
Programs don't have a metric function .
The main construction issue is to drill two straight , parallel holes to lock the shafts in and that the shafts be very accurate in diameter and straightness.
The larger diameter chrome plated shafts out of old inkjet and laser printers are very straight and precise in diameter over the short distance required .
I have not given dimensions as you have to make it to fit your compound slide and models vary greatly .
There is many ways it could be made and still work fine.
Mine is a prototype I nocked up out of scrap and intended to make a pretty one out of alloy but it works good so I have not bothered.
Hope I have shed some light on the situation. Best regards Retromilling

Keith_W
7th Oct 2008, 06:10 PM
Thanks Retromilling for the great post, pictures and taper zip files.
Have saved your post in my Projects File and will be makeing on up in the near future,

Regards,
Keith.

Retromilling
8th Oct 2008, 09:42 AM
Thanks Kieth, you are most welcome. I find it quite handy and mine gives a more accurate taper than I can get offsetting the tailstock which is a real pain .