Request for Assistance for Projection Calculations for the T-4

[jturner421]

In a previous post: https://forum.tormek.com/index.php?topic=4216.0 I asked about using the TTS-100 to set a consistent distance from the USB to the grinding stone.  I created a prototype jig that sets chisel projection at 43mm @ 25 degrees and 37mm @ 30 degrees using the SE-77 when measured from the top portion of the jig to the end of the chisel. The AngleMaster WM-200 was used to check the grinding angle. The projection jig sits against the bottom clamping plate of the SE-77.  Based on my measurements, the bottom plate is inset 2mm from the top plate.   

Looking on the forums, there is a tremendous amount of information about calculating the proper projection and USB height for knife sharpening, less so for chisel and planes, and no data applicable to the T-4. Rather than recreate the wheel—no pun intended—I'd like to either extend the TormekCalc spreadsheet to cover the SG-200 and leather wheel for the T-4 or if there is enough interest, set up a online calculator that everyone can use.

I know that Jan has a program he uses to check projection and angles that is tuned to the SE-76.  Does anyone know what formula(s) is used for that calculation and what are the relative input values that I should measure on the SE-77 jig and T-4?

[cbwx34]

In a previous post: https://forum.tormek.com/index.php?topic=4216.0 I asked about using the TTS-100 to set a consistent distance from the USB to the grinding stone.  I created a prototype jig that sets chisel projection at 43mm @ 25 degrees and 37mm @ 30 degrees using the SE-77 when measured from the top portion of the jig to the end of the chisel. The AngleMaster WM-200 was used to check the grinding angle. The projection jig sits against the bottom clamping plate of the SE-77.  Based on my measurements, the bottom plate is inset 2mm from the top plate.   

Looking on the forums, there is a tremendous amount of information about calculating the proper projection and USB height for knife sharpening, less so for chisel and planes, and no data applicable to the T-4. Rather than recreate the wheel—no pun intended—I'd like to either extend the TormekCalc spreadsheet to cover the SG-200 and leather wheel for the T-4 or if there is enough interest, set up a online calculator that everyone can use.

I know that Jan has a program he uses to check projection and angles that is tuned to the SE-76.  Does anyone know what formula(s) is used for that calculation and what are the relative input values that I should measure on the SE-77 jig and T-4?

Not really my area... so I'll just pass this along, in hope it helps.

Quite a bit of discussion here:  https://forum.tormek.com/index.php?topic=4116.0

The TormekCalc2 calculator has the SE-77 as an option under the "Jigs" tab... so maybe that will calculate it?  (If not, still a good reference for measurements, formulas, etc.).  https://forum.tormek.com/index.php?topic=4181.0

p.s.  If you measure directly to the wheel to set the USB, which machine you're using doesn't matter.

[Ken S]

Joel,

I think the easiest way to answer your questions is to think of the T4 as a T8 with the diameter of the grinding wheel worn down to 200mm.
With the Anglemaster, the only change when going from the T8 to the T4 is resetting the wheel diameter from 250mm to 200mm (including adjusting for wheel wear.)
The two small metal wheels on the TTS-100 automatically compensate for changes in wheel diameter, either for wear or switching back and forth between the T4 and T8. I chose to use the TTS-100 for chisels and bench plane blades for simplicity. Using the B hole sets the Distance between the support bar and the grinding wheel. If you sharpen just chisels and plane blades, you can set this once and probably never need to reset it. If you do reset the Distance for other tools like knives, using the hole makes accurate resetting essentially immediate and automatic. Do not get hung up worrying about wheel wear. Formost of us, sharpening chisels and plane blades, once a year is often enough to check it.
Once the Distance is set, I set the Projection using the Anglemaster. The Anglemaster works very well with a large flat plain like the back of a chisel or bench plane blade. It works even better if you have good light.

I place a blank piece of white labelmaker tape in one of the three slots of the TTS-100. With the chisel or plane blade still set in the SE jig, I hold it against the slot of the TTS-100 and mark the Projection with a fine point Sharpie. I note the degree setting from the Anglemaster on the labelmaker tape next to the Projection mark.

I made several angle Projection marks on the labelmaker tape. As a general rule, I only use 25°. That works well with my older, high carbon steel tools. I generally work with pine or poplar. If I ever use the few A2 steel chisels I have accumulated over the years, I will switch to 30°.

Using the TTS-100 this way, I can switch back and forth between the T4 and T8 with no adjustments.

I had the rare opportunity of being able to compare the T4 and T7 side by side at leisure. They are strikingly similar. Just think of the T8 as essentially a T4 with a 250mm grinding wheel and vise versa.

Ken

[Jan]

Joel,

please read https://forum.tormek.com/index.php?topic=2731.msg14621#msg14621

It should work for T4 also. Use basic setup of SE-77 and ignore possible differences between SE-77 and SE-76.

Jan

[Dutchman]

... snip
Does anyone know what formula(s) is used for that calculation and what are the relative input values that I should measure on the SE-77 jig and T-4?

The original source of mathematics for calculating the settings can be found in the link below in my "signature".
AND as CBWX34 says above:
"If you measure directly to the wheel to set the USB, which machine you're using doesn't matter."

[jturner421]

I appreciate all the responses. I'm think I'm making this more complex than it needs to be so. After trying a few different setups today, I'm setting on a workflow that will likely replace my waterstones while in the shop for sharpening. 

Using the TTS-100 for both the SG-200 and honing wheel eliminates any guesswork in setting the USB distance.  I've rounded out my collection of projection jigs to get a repeatable projection for the SE-77 at 20, 25, 30, and 35 degrees.  Setup is quicker than using my Veritas jig and stones.

One area that I'm experimenting with is grinding a few of my chisels at 25 degrees with the stone set to coarse and a small secondary bevel at 30 with the stone set at fine.  My thought is that when it comes time to touch up, a few seconds at the fine stone setting with a quick touchup with the leather wheel and I'm back to work.  After 5 -7 times, I'll have to regrind the primary bevel.  I can also quick change the edge for different woods (softwoods vs hardwoods) and tasks if need be, as opposed to regrinding the entire bevel if I want to setup a chisel for a chopping session.