ID grinding spindles, quills and bits

[TorontoBuilder]

So, I have a tool post grinder. It is missing the ID grinding accessory quill. It is supposedly just the one shown below.

The external grinding wheel hub is supposed to detach and the extension is then mounted in its place. This does not seem like it would be very precise and must rely on dressing the stone significantly in order to true things up.

ID grinding wheels up to 1" in diameter can then be mounted as shown. This is a very limited design in that small diameter wheels cannot be mounted. There is also the risk the wheel can be cracked while tightening it onto the quill. But it would be very easy to make an extension.

However, I'd really like easy to swap quills that are affixed to the spindle via a taper, or a locator shaft with threaded end as shown below:

The upper version looks perfect, except I can't find small diameter grinding bits mounted on threaded arbor like is shown. Anyone seen such animals around for purchase? I can find abrasives cones that would glue on like shown in the lower version but the selection I've found at KBC is limited

Next question, if I make quills and bore and ream the end to common grinding point diameters 1/8, 1/4 etc, what is likely better mounting method... heat shrink fitting, Loctite red adhesive, or CA glue? The bore for the shank will be deep enough so that the abrasive sits very close to the end of the quill. I want to use diamond and borazon bits that can't be dressed to run true so the mounting method must be as precise as possible.

For the above reason I'm leaning towards either buying, or making a second spindle that fits the tool post grinder bore. Anyone know a source for affordable belt drive spindles, either with a collet, or a threaded locator bore as I've shown?

 

[PeterT]

So, I have a tool post grinder. It is missing the ID grinding accessory quill. It is supposedly just the one shown below.
For the above reason I'm leaning towards either buying, or making a second spindle that fits the tool post grinder bore. Anyone know a source for affordable belt drive spindles, either with a collet, or a threaded locator bore as I've shown?

Not really answering your questions directly, but a few thoughts

You can make grinding stones from surface grinding wheels wheels to suite your application. I sent a CAD file to a water jet cutter. These were 1/4" thick but I think the kerf was acceptable, you could make them from thicker wheels. (Advice caveat: don't shoot your eye out & don't sue me if you do). Alternatively I made a wheel using diamond core & drill bit. It works but its tedious, need water slurry etc. I was more concerned about leaving stress fractures. I have successful bonded & ran a ~ 20mmOD x 10mm ID dia stone to a steel arbor with epoxy. Dan Gelbart did the same thing in one of his videos. I don't think the adhesive of commercial stones is much different, but again, be careful because smaller stones might call for 30-40K rpm.

In terms of arbors all I can say is they must be dead nuts accurate & balanced if they are say > 4:1 aspect ratio (length : diameter) if they doing any more than say 20K rpm. I think high tensile material is called for. Retrofitting existing grinders with proprietary tapers & threads is not a lot of fun (ask me how I know).

Personally I will probably go in this direction. If one can trust the stated runout & bearings & heat & all that, it seems like a relatively straightforward matter of holding a dedicated wheel/arbor which looks remarkably like a hunk of straight shaft . But I don't see many out there in the wild, so maybe there is a reason. I guess if the grinding experiment doesn't work, sell it to a CNC router guy to recover capital.

 

[TorontoBuilder]

Not really answering your questions directly, but a few thoughts

You can make grinding stones from surface grinding wheels wheels to suite your application. I sent a CAD file to a water jet cutter. These were 1/4" thick but I think the kerf was acceptable, you could make them from thicker wheels. (Advice caveat: don't shoot your eye out & don't sue me if you do). Alternatively I made a wheel using diamond core & drill bit. It works but its tedious, need water slurry etc. I was more concerned about leaving stress fractures. I have successful bonded & ran a ~ 20mmOD x 10mm ID dia stone to a steel arbor with epoxy. Dan Gelbart did the same thing in one of his videos. I don't think the adhesive of commercial stones is much different, but again, be careful because smaller stones might call for 30-40K rpm.

In terms of arbors all I can say is they must be dead nuts accurate & balanced if they are say > 4:1 aspect ratio (length : diameter) if they doing any more than say 20K rpm. I think high tensile material is called for. Retrofitting existing grinders with proprietary tapers & threads is not a lot of fun (ask me how I know).

Personally I will probably go in this direction. If one can trust the stated runout & bearings & heat & all that, it seems like a relatively straightforward matter of holding a dedicated wheel/arbor which looks remarkably like a hunk of straight shaft . But I don't see many out there in the wild, so maybe there is a reason. I guess if the grinding experiment doesn't work, sell it to a CNC router guy to recover capital.
View attachment 56025

Nice with the waterjet cut stones. May be a possibility.

I have never gotten a good response about the runout of those spindle motors, but I will be buying one for my cnc router, so I can test one then. I also know I can make extensions that fit the collet taper so that may be an option.

I do have a line on an affordable OEM spindle but I dont know enough about the spindle bore... I should just bite the bullet and buy it and then see what I can do. I have so many projects that require precision grinding I am willing to spend a little to find what works best

 

[RobinHood]

Your thoughts & design are more or less in line with how Dumore builds their TPGs.

Their smallest one has an integral spindle with various adapters to hold a variety of mounted points / small grinding wheels. The more components get “added” the more the run-outs stack up, even at very tight sliding fit registers.

Cracking the stones during installation is a valid concern. In practice, it’s not really a problem as no grinding wheels should ever be gronked onto any spindle. Just enough torque to compress the blotters. All the tightening torque has to resist is the initial acceleration of the wheel. Once you are grinding, the system is self tightening, hence the LH / RH threads of the retaining screw (depending of course on the direction of spindle rotation).

The larger Dumore grinders use cartridge spindles of different designs &/or an adapter for mounted points. You can see the one spindle has a very long nose; it takes the smallest grinding stones they make. Anything smaller needs a mounted point held in a collet adapter (black item)

Examples of some tiny grinding wheels.

The smallest wheels I have are 1/4” nominal - dressed to even smaller diameter. The physical limit is basically your spindle diameter / retaining screw head diameter. The operational limit soon becomes the max spindle rpm; ie, not fast enough - even at 40k rpm!

Any place that sells Dumore products (or equivalents) can help you out with small grinding wheels and mounted points.

 

[TorontoBuilder]

Thanks @RobinHood for the feedback and excellent pics. I'm not jealous at all

 

[TorontoBuilder]

Sooooo......

In all my googling, and searching I found the current owner of Duplex IP Jena Tec. They're still in business, and still selling the D27 grinder. They also sell many other spindles.

But they have almost no information available at all beyond the most basic stuff. I couldn't even find the cost of the grinder new, but I know it is not cheap. Their TPG catalog lists several optional long reach spindles. But little good info on them and as I later found out, not nearly all the spindles they had at one time.

I looked at their spindle catalog and found they have a lot of GS belt driven spindles too. I found one that should fit the D27 but they jave no data on whether they do or not... and little on what quill style it uses.

Then I found that KBC sells duplex long reach spindles of different varieties. I scrounged thru the listings to see if any fit the D27 and found one. Despite the lack of good info I bought it

Duplex long Reach Spindle for D27 grinder.

For interchangeable extensions.

FEATURES:

• Scope – For grinding of small bores to tight limits of accuracy and finish. Fitted with special high precision matched bakelite caged bearings assembled in preloaded pairs, and are suitable for continuous running.
• Non-stick taper for extension spindles for the wheels.
• Extension is included. Remember, always choose the shortest extension that will do the job.
• Lubrication – By oil mist. Bearings are protected by labyrinth seals and revolving baffles. Bearing preload automatically adjusts the radial and end clearances and accommodates shaft expansion.

Cant find this in the Jena Tec catalog anywhere