# Dumore tool post grinder adapted to use Sioux valve seat grinding stones



## John Conroy (Oct 28, 2022)

I’ve had this vintage Dumore tool post grinder for years now and have never used it because I never got around to finding a supply of grinding stones for it. I have a large selection of Sioux vavle seat grinding stones. They get threaded onto a driver that has 11/16-16 threads. They are readily available in a variety of sizes, grits and compounds. The Dumore has a ¼” straight shaft that their stones slide on to and are retained by a nut and washer.





















The Dumore stones have a metal sleeve bonded into the center that fits accurately onto the shaft. I made the adapter using a short piece of ¾” drill rod and single pointed the 11/16 thread then drilled and reamed the ¼” bore.


















To try it out I selected a ruby general purpose Sioux stone and held the diamond truing point in an ER40 collet to true the stone to the lathe cross-slide axis.







I mounted the 12” shop made table for my Vertex super spacer and proceeded to try and remove the .008” of flatness run-out from it’s surface. This table was a salvage piece that had some brackets welded onto it. After I cut off the brackets I tried turning it flat in the lathe with carbide tooling but the hard spots left by the welding resisted everything I tried, the carbide cutters would deflect over the hard spots. I thought grinding might be the answer.
















It was very slow going. After some trial I settled on 225 RPM lathe spindle speed and a very slow feed rate of .007” per revolution of the spindle. Depth of cut maximum per pass was .0005”
This was the result after 4 passes.










After 20 passes.





After I lost track of how many passes I still had 1 stubborn low spot right between 2 large weld areas.





After many boring hours finally success! The surface now has just a couple of tenths deviation no matter how I measure it.


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## John Conroy (Oct 28, 2022)

I also got around to correcting the .002" dish shape of my faceplate. In the video you can hear how the grinder slowly bogs down as it moves outward. Sorry about the shoddy video camera work. This happens as it struggles to deal with the progressively higher SFPM.

After 1st pass you can see the stone is just touching on the outside of the faceplate and moves further inward as the pics move down. This took 20 passes. I increased the feed rates and switched to a larger stone.


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## PeterT (Oct 28, 2022)

Nice work John. Perfect application for TPG. Now you have nice straight reference surfaces.
I was able to true my CI slotted plate with cutting tools but they were not happy with the interrupted cuts across the slots & what I suspect were harder crunchy bits in the metal.
Sourcing stones for TPG can be a headache, but from what I have seen of the Dumore vs Themac, I think Dumore is more adaptable. Themacs have their own propriety arbor taper/dimensions which is a pita to replicate for custom tools.


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## gerritv (Oct 28, 2022)

Dumore stones are available from https://bdiexpress.com in Canada. Balanced out of the box.


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## Proxule (Oct 28, 2022)

Impressive work!
Perhaps this is the method we can use for my valves?
Hats off to you!


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## Susquatch (Oct 28, 2022)

John Conroy said:


> I also got around to correcting the .002" dish shape of my faceplate.



Excellent work John. 

A testament to your expertise, and your patience!


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## Canadium (Oct 28, 2022)

gerritv said:


> Dumore stones are available from https://bdiexpress.com in Canada. Balanced out of the box.


Went to this site but couldn't find the product. What are your search terms? Search for Dumore comes up empty.


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## little ol' e (Oct 28, 2022)

Things always get interesting in the shop once innovation takes over the brain. 
Nice set-up for grinding. I see you covered the ways as well, top notch work with expertise built in!


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## gerritv (Oct 28, 2022)

Canadium said:


> Went to this site but couldn't find the product. What are your search terms? Search for Dumore comes up empty.


Sorry, it is https://shop.emprecise.com/catalogue/product/457574


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## Canadium (Oct 28, 2022)

gerritv said:


> Sorry, it is https://shop.emprecise.com/catalogue/product/457574


Thats almost next door to me! I'll have to pay them a visit some time! Thanks @gerritv


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## John Conroy (Oct 29, 2022)

My grinder is a model 11 and no longer in production. It's missing a bunch of parts including the wheel flanges required when using Dumore straight wheels and the adapter chucks for mounting small wheels and points for doing internal grinding. More research will be required on my part before I could use the one genuine Dumore wheel I have. The Sioux stones are familiar to me and have a safe operating speed beyond the capability of my grinder with the pulleys I have so I feel safe in using them. A grinding stone exploding at 15000 rpm is a scary thing.
The current Dumore model 44 seems to be the closest to the size and power to mine. If anyone knows where I could find a copy of the user manual for the model 11 I would appreciate a heads up. The manual for the model 44 is available for download on the Dumore site and looks like it was first published in 1940, about the time the model 11 was sold LoL.


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## John Conroy (Oct 29, 2022)

This info is from the Dumore site and very good to have before starting to use a TPG. Dumore doesn't seem to talk about face grinding,  only cylindrical. The big difference is that the SFPM changes when face grinding. If I do something like this again I'll try using the VFD to change the spindle speed as the cross slide moves in or out in order to compensate for this.

Workpiece Speed & Direction - Tool Post Grinders​For cylindrical tool post grinding, the usual work speed range is 50 to 90 sfm. Typically, a work speed of about 50 rpm works well for most grinding operations. However, this speed can be varied to meet many grinding conditions.
If the grinding wheel glazes (the grains dull before the bond wears), the wheel is too “hard” for conditions. A reasonable variation in apparent wheel grade can be compensated by varying work speed. By increasing the workpiece rpm, the wheel will provide a “softer” action because it must now remove more material per wheel revolution. This increases the cutting force per grain, so the grains are more readily broken off, thus exposing new sharp grains and keeping the wheel from glazing.
Conversely, a grinding wheel that is loading (bond wears before grain dulls) is too “soft” for conditions. This can be remedied to some degree by decreasing speed, so the wheel cuts less material per wheel revolution. As a result, the grains are less readily lost, making the wheel seem “harder”.
External grinding is done with the work rotating in the same direction as the grinding wheel, while internal grinding is done with the work rotating in the opposite direction. In both cases, the result is the contact faces of the work and wheel moving in opposite directions, thus maximizing cutting action.


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## little ol' e (Oct 29, 2022)

Some really good information in this post, will certainly come in handy for me in the future. I don't get time to U-tube much, thank you for posting.


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## gerritv (Oct 29, 2022)

Here's the manual and a drawing of the chuck. I haven't made the chuck yet. I can measure the wheel washers if you like.
I bought new brushes from Asia, had to file one side down slightly for it to fit. Belts were ordered from the UK: https://beltingonline.com  12.5mm wide, 420 mm long. New bearings purchasesd from https://bocabearing.com although they have rubber seals so heat up at the high RPM setting. If I use it at that speed I will be removing the seals and going back to oil in the housing. I couldn't find metal seal bearings, the originals were open on both sides. They also have the motor bearings. Shipping is $0 from US!


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## historicalarms (Oct 29, 2022)

All the old British "How To" books ive read claim proper faceplate contour is a .002 dip into the center....i could never understand the concept of why that was "better" than true & flat.


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## PeterT (Oct 29, 2022)

I've read about that dip rule of thumb too. I recall finding a reasonable explanation but it evades me now. But I've also see the equivalent thing being measured & checked on a modern CNC & they seemed to be striving for perpendicular to bed.

In another post where Crispin is re-grinding his spindle nose, he does mention that the TPG spindle is probably not optimal for axial load vs radial load as a function of the bearings. He dish profiles the end of solid stone as a cup & grinds the spindle datum face. But maybe like most things, a little bit of load is probably fine vs lots (whatever that means) might start heating/wearing the bearings? Grinding is a power intensive removal process, I suspect the sparks & pucker factor might be limiting before this point occurs, but I dunno.

I've thought about buying a CNC spindle motor + VFD combo with ER collet to act as an small footprint type grinder. Presumably if it can handle radial & axial 'milling mode' loads it could also grind? You get a smooth running 3 phase brushless motor which is nice. Bu IMO it all boils down to the bearings & that's where things get kind of grey & mysterious with the offshore units. I'd be happy if they were lower quality AC, just replace them as needed for the little bit of work I would do. But often the integrated spindle assembly are combinations of radial bearings, or require water cooling on the unit or... Too many unknowns for the $ factor unless I see a working example.


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## DPittman (Oct 29, 2022)

PeterT said:


> I've read about that dip rule of thumb too. I recall finding a reasonable explanation but it evades me now. But I've also see the equivalent thing being measured & checked on a modern CNC & they seemed to be striving for perpendicular to bed.
> 
> In another post where Crispin is re-grinding his spindle nose, he does mention that the TPG spindle is probably not optimal for axial load vs radial load as a function of the bearings. He dish profiles the end of solid stone as a cup & grinds the spindle datum face. But maybe like most things, a little bit of load is probably fine vs lots (whatever that means) might start heating/wearing the bearings? Grinding is a power intensive removal process, I suspect the sparks & pucker factor might be limiting before this point occurs, but I dunno.
> 
> I've thought about buying a CNC spindle motor + VFD combo with ER collet to act as an small footprint type grinder. Presumably if it can handle radial & axial 'milling mode' loads it could also grind? You get a smooth running 3 phase brushless motor which is nice. Bu IMO it all boils down to the bearings & that's where things get kind of grey & mysterious with the offshore units. I'd be happy if they were lower quality AC, just replace them as needed for the little bit of work I would do. But often the integrated spindle assembly are combinations of radial bearings, or require water cooling on the unit or... Too many unknowns for the $ factor unless I see a working example.


I've been waiting for you Peter to figure this all out and make your own so I could copy what you did.  I know I'm unlikely to do it right unless I'm copying g someone's else's desig  that was smarter than me.


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## PeterT (Oct 29, 2022)

I need more data (or money LOL). OTOH, my buddy ground a main shaft for his model turbine using what looked like a pretty rudimentary old school spindle, compound set at shallow angle on medium size Emco lathe, indicator setup etc. He got it to the target tenth dimension & with appropriate finish for bearing fit & whatnot. The engine happily spins at 80K, so I guess there there are multiple ways to skin the cat. He also had prior familiarity with this level of grinding from his former career.


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## YYCHM (Oct 29, 2022)

PeterT said:


> I need more data (or money LOL). OTOH, my buddy ground a main shaft for his model turbine using what looked like a pretty rudimentary old school spindle, compound set at shallow angle on medium size Emco lathe, indicator setup etc. He got it to the target tenth dimension & with appropriate finish for bearing fit & whatnot. The engine happily spins at 80K, so I guess there there are multiple ways to skin the cat. He also had prior familiarity with this level of grinding from his former career.



What model Turbine?  Need pictures please.


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## PeterT (Oct 29, 2022)

Tractor museum ends summer season
					

Dave Pape brought with him a home-built miniature jet engine, which he fired up for the crowd of 20 people on the tractor museum Aug. 31.




					www.townandcountrytoday.com


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## John Conroy (Oct 29, 2022)

gerritv said:


> Here's the manual and a drawing of the chuck. I haven't made the chuck yet. I can measure the wheel washers if you like.
> I bought new brushes from Asia, had to file one side down slightly for it to fit. Belts were ordered from the UK: https://beltingonline.com  12.5mm wide, 420 mm long. New bearings purchasesd from https://bocabearing.com although they have rubber seals so heat up at the high RPM setting. If I use it at that speed I will be removing the seals and going back to oil in the housing. I couldn't find metal seal bearings, the originals were open on both sides. They also have the motor bearings. Shipping is $0 from US!


Thanks for those documents and info Gerrit, I would appreciate it if you could provide the dimensions of the flange washers.  The belt with my machine is a toothed timing belt of some kind, run with the teeth facing out.  The dimensions you provided will help me track down a correct one.


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## Susquatch (Oct 30, 2022)

John Conroy said:


> The belt with my machine is a toothed timing belt of some kind, run with the teeth facing out.



This is very curious to me John. What in the world is the purpose of facing the teeth out? On the surface that would appear to negate the timing aspect and probably accelerate belt wear too.


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## gerritv (Oct 30, 2022)

These are driven by flat belts. Dumore hasn't sold this belt for a long time. I suppose sometmes any belt is better than no belt.


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## Susquatch (Oct 30, 2022)

gerritv said:


> These are driven by flat belts. Dumore hasn't sold this belt for a long time. I suppose sometmes any belt is better than no belt.



I see, so basically you are suggesting that a reversed timing belt was used to substitute for a flat belt that was no longer available and the timing feature isn't used. 

The back side of a timing belt isn't very durable. It's not designed to run against a pulley of any kind. When one is located, I'd be tempted to buy a box of them.....


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## gerritv (Oct 30, 2022)

its just plain wrong to do this. A flat belt conforms slightly to the crown of the pulley, thus tracking properly. And it is considereably more flexible than a toothed belt.

I bought 2 just in case but seeing how they are constructed I can't imagine wearing one out. The original Dumore ones might be flimsier, never seen one. I know that at Univac we used a lot of flat belts for driving pulleys on card sorters and readers. Nothing like merging 2 sets of cards at 1000 cpm each into a centre pocket.


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## gerritv (Oct 30, 2022)

John Conroy said:


> Thanks for those documents and info Gerrit, I would appreciate it if you could provide the dimensions of the flange washers.  The belt with my machine is a toothed timing belt of some kind, run with the teeth facing out.  The dimensions you provided will help me track down a correct one.


5/32" thick, 1.044" diameter. there is a recess 0.015" deep, .77" diameter on one side (side where it touches the grinding wheel). Other side has a tapered face. Hole is 0.250" diameter, should be a close fit on the shaft. Everything should be concentirc to avoid imbalance.


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## Susquatch (Oct 30, 2022)

gerritv said:


> its just plain wrong to do this. A flat belt conforms slightly to the crown of the pulley, thus tracking properly. And it is considereably more flexible than a toothed belt.



Yup. Now have a boo at the fabric material used on the back of a timing belt. It won't last long!


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## John Conroy (Oct 30, 2022)

Thanks again Gerrit. The inside out toothed belt actually runs very smoothly and conforms to the crowned pulleys well but since this grinder has no belt guard I think a correct belt is in order.LoL


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## RobinHood (Oct 30, 2022)

I would contact Transmission Supply Edmonton for the flat belt. This is where I got mine for the Dumore #44 and the Clarkson T&C Grinder. (The Calgary branch actually - but the belts were in stock in Edmonton, so they shipped them here). I basically just gave them the dimensions and they cut them off of stock material (to any width you want). Runs very smoothly and seems very durable. Megadyne / Jason, made in Italy. Very good price too.

The first picture is the original Dumore belt; the second is of the equivalent replacement.











Here is the old and new belt to the Clarkson T&CG.


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## PeterT (Oct 30, 2022)

This belt issue comes up a lot with Themac TPGs as well, although the belts are still available for current models. They are very thin & have some kind of fiber in them very similar to @RobinHood pics. 
Supposedly the low mass & material factors in them staying put at speed & not transmitting vibration into the spindle. I've heard or read that 'regular' belts (whatever that means) start to arc & stretch under their own weight at TPG like rpm/pulley conditions or develop harmonics. Supposedly vacuum cleaner belts are similar but who knows about size & equivalent power, configuration etc.


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## Darren (Oct 31, 2022)

I've wanted a TPG for a while now, and won this guy tonight. Model 8119, catalog number 31-011, 1/5th hp. Is that similar to yours @John Conroy, @RobinHood  ?









						#586 Dumore Tool Post grinder in case NICE!! 31-011  | eBay
					

READ THIS! I AM hard to get ahold of --but am reachable. You generally won't be able to reach us on weekends. We work gun shows, and try to travel then. WE WILL send you a combined invoice.



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I found the manual: http://vintagemachinery.org/pubs/detail.aspx?id=19657

It says 8-11 inch swing. I'm hoping it will work ok with my 13" Emco.


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## YYCHM (Oct 31, 2022)

Does not ship to Canada ?


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## Darren (Oct 31, 2022)

i live a short drive to the border and have an address there. Rydens border store.


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## John Conroy (Oct 31, 2022)

It looks very similar to my model 11, maybe yours is newer. Mine doesn't even have a switch, you just unplug to turn it off. The specs on your motor are the same as mine. I found a local source for belts and ordered 3. I'll report on them when they arrive.


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## Darren (Oct 31, 2022)

If I recall, you have a 14" swing machine @John Conroy ?


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## John Conroy (Oct 31, 2022)

That's right. I used shims to get the TPG spindle on center with the lathe spindle


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## Darren (Oct 31, 2022)

Awesome, Thank you for the pics. 

I almost won another TPG a while back but i'm glad I didn't.  I think it was 1/2hp and it weighed like 60 lbs, so i think it would have been much too large. 

I want to make a D1-4 camlock rotary table adapter and after the Mr Crispin video, I see that grinding is probably the way to go.


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## RobinHood (Oct 31, 2022)

Nice score, Darren.

It is very similar in size to my #44. I use it on all lathes.

As John shows, just shim the mounting post to get to center height.


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## Susquatch (Nov 1, 2022)

John Conroy said:


> That's right. I used shims to get the TPG spindle on center with the lathe spindle



Hey John, just wondering about a few things.

Given that both the lathe and the grinder are cylindrical devices, does it really matter if the grinder axis isn't the same exact height as the lathe? I would think +/- 20 degrees or so would work just fine. I chose a degree qualifier simply to take into account the height impact of a smaller diameter part.

I notice that your belt appears to be a backward timing belt. I believe you previously mentioned that, but I don't recall if you told us how well the belt backing fabric is holding up.


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## John Conroy (Nov 1, 2022)

I'm not sure if there would be a problem running the TPG spindle at a different height that the lathe. The instruction manuals I read on the Dumore site all say they must be the same height. I suspect the TPG bracket that sits on the compound is designed to be loaded 90 degrees to the compound mounting stud. If the TPG is above or below center the loading would be diagonal and the bracket is not very robust.

The inside out toothed belt tracks perfectly and runs very smooth. In the last week I have run it about 10 hours and have not had a single issue with slipping, tracking or vibration. I think I will attempt to copy the belt guard used on later models as it would be a disaster to get fingers into the belt area when running.


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## gerritv (Nov 1, 2022)

Its a 11-011, not a 31. But in great looking condition. Manual and other parts info is in an earlier post in this thread..

For straight grinding the centre height doesn't matter much, for taper grinding I think you end up with a not-straight surface, I recall making that mistake once when truing up  an ER11 collet chuck.


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## DPittman (Nov 1, 2022)

John Conroy said:


> That's right. I used shims to get the TPG spindle on center with the lathe spindleView attachment 27551View attachment 27552View attachment 27553View attachment 27554


Would a TPG loose functionality if it could not pivot on top of the compound and was instead fixed in one position on the compound?


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## Darren (Nov 1, 2022)

gerritv said:


> Its a 11-011, not a 31. But in great looking condition. Manual and other parts info is in an earlier post in this thread..
> 
> For straight grinding the centre height doesn't matter much, for taper grinding I think you end up with a not-straight surface, I recall making that mistake once when truing up  an ER11 collet chuck.


I thought it was 11, but its hard to see clearly.  Thanks.

For taper grinding the two spindle centerline would have to be on the same level plane to avoid introducing an error.  Same as when indicating a taper.


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## Susquatch (Nov 1, 2022)

John Conroy said:


> I'm not sure if there would be a problem running the TPG spindle at a different height that the lathe. The instruction manuals I read on the Dumore site all say they must be the same height. I suspect the TPG bracket that sits on the compound is designed to be loaded 90 degrees to the compound mounting stud. If the TPG is above or below center the loading would be diagonal and the bracket is not very robust.
> 
> The inside out toothed belt tracks perfectly and runs very smooth. In the last week I have run it about 10 hours and have not had a single issue with slipping, tracking or vibration. I think I will attempt to copy the belt guard used on later models as it would be a disaster to get fingers into the belt area when running.



In hind sight, I think high could be a fiasco waiting to happen if either drive stalled or the stone grabbed. On the other hand, low should work fine. But all assessed in my head so definitely not advice to anyone else. Just my curiosity and challenging assumptions at work again. 

Glad the belt is working for you. I'm prolly just biased by the number of automotive timing belts I've seen that failed from the outside in. In fact, now that I think about it, that's how the timing belt on my Hartford Mill was failing. I kept it as a backup - no comments from the peanut gallery..... When I get back to the shop, I'll post a photo.


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## Susquatch (Nov 1, 2022)

Darren said:


> I thought it was 11, but its hard to see clearly.  Thanks.
> 
> For taper grinding the two spindle centerline would have to be on the same level plane to avoid introducing an error.  Same as when indicating a taper.



Agreed. Not sure I'll ever grind a taper though.


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## John Conroy (Nov 1, 2022)

DPittman said:


> Would a TPG loose functionality if it could not pivot on top of the compound and was instead fixed in one position on the compound?


It needs to be able to pivot in order to be versatile. When I did the grinding on the 12" round plate I had to experiment with the angle so I would be able to traverse the entire face of the plate with the available cross slide travel on my lathe. Once that angle was determined I trued the stone face to be parallel to the plate using a diamond point.


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## Darren (Nov 1, 2022)

Susquatch said:


> Agreed. Not sure I'll ever grind a taper though.


It would be nice for making batches of R8 tooling for example. Once you fine tune the taper you could grind a bunched of roughed in parts at once between centers. Last one I did with just the lathe was a bit of a challenge to get the taper just right.


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## PeterT (Nov 1, 2022)

Susquatch said:


> In hind sight, I think high could be a fiasco waiting to happen if either drive stalled or the stone grabbed. On the other hand, low should work fine. But all assessed in my head so definitely not advice to anyone else. Just my curiosity and challenging assumptions at work again.


Generally the TPGs only have one motor direction dictated by the arbor threads. But sometimes one may find himself on the other side of spindle maybe depending on reach or angle orientation. The lathe can be reversed to oppose the grinder ok, but if you consciously positioned the grinding wheel high or low for some reason, this reorientation without confirming center height might be an example situation of bad things happening if the stone tried to walk up the part.


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## Susquatch (Nov 1, 2022)

PeterT said:


> Generally the TPGs only have one motor direction dictated by the arbor threads. But sometimes one may find himself on the other side of spindle maybe depending on reach or angle orientation. The lathe can be reversed to oppose the grinder ok, but if you consciously positioned the grinding wheel high or low for some reason, this reorientation without confirming center height might be an example situation of bad things happening if the stone tried to walk up the part.


Yup, my thinking exactly.


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## John Conroy (Nov 9, 2022)

I received the belts I ordered from The Belt Shop in Edmonton. I talked to Myron there and gave him the width and length supplied by Gerrit and told him it was for a Dumore tool post grinder. I hadn't yet seen the belt that Rudy posted but the belts he supplied are the same type. They are thinner and more pliable than the old belt.


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## trlvn (Nov 10, 2022)

John Conroy said:


> I received the belts I ordered from The Belt Shop in Edmonton. I talked to Myron there and gave him the width and length supplied by Gerrit and told him it was for a Dumore tool post grinder.


If you don't mind, how much did they charge?  Was it a long turnaround?

I need a belt for the old Tom Thumb grinder if I ever get around to restoring it.

Craig


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## John Conroy (Nov 10, 2022)

They were $22 each. I bought 3, more than a lifetime supply I'm sure.


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