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

John Conroy

John Conroy

member
Premium Member
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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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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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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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!
 
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.
 
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.
 
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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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.
 
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.
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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.
 
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.
 
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.
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What model Turbine? Need pictures please.
 
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