# Tool post grinding wheel dressing apparatus



## petertha (Mar 15, 2020)

I made this up from steel bits & pieces. My idea was to have something which was preset to spindle center so it can be temporarily clamped on to lathe bed, dress the wheel then removed & get back to grinding. The diamond tool is the kind bonded into the tip of a 0.375" diameter shank available at most tooling suppliers. (Yes the lathe bed is all covered up when dressing & grinding, just removed for pics).


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## Bob Korves (Mar 15, 2020)

Typically, the dressing tool is mounted to the tool post grinder assembly so the wheel can be dressed parallel with the spindle, making a dead accurate dress without any measuring and without the setup changing as you move the compound and other axes to new positions.  Tapered grinding wheels are not often needed or desired for tool post grinding, never in my experience.


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## benmychree (Mar 15, 2020)

Never seen such a dressing device, Bob, pictures?


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## Bob Korves (Mar 15, 2020)

benmychree said:


> Never seen such a dressing device, Bob, pictures?


No, John.  Just thinking out loud, and maybe not thinking hard enough before hitting the "post" button...


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## benmychree (Mar 15, 2020)

Shouldn't you be out in your new shop-to-be arranging stuff instead of sitting in front of the computer ---- shouldn't I be doing the same?  Too darn cold in mine!


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## petertha (Mar 15, 2020)

Not quite sure I follow you Bob. With the dressing tool fixed to lathe bed, the carriage is traversed. TPG is mounted to compound, but compound is always locked, so TPG goes along for the ride so wheel gets dressed parallel to spindle axis. I move the cross bed travel inward to dress using DRO as guide (and then re-zeroed). 

Maybe what you are getting at is I don't have control over the amount of grinding wheel removal relative to last position? The only way I'v eseen that done is something mounted on or in the chuck (which is not great if you have work in the chuck). If you have some pictorials that would be great.


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## Bob Korves (Mar 15, 2020)

petertha said:


> Not quite sure I follow you Bob. With the dressing tool fixed to lathe bed, the carriage is traversed. TPG is mounted to compound, but compound is always locked, so TPG goes along for the ride so wheel gets dressed parallel to spindle axis. I move the cross bed travel inward to dress using DRO as guide (and then re-zeroed).
> 
> Maybe what you are getting at is I don't have control over the amount of grinding wheel removal relative to last position? The only way I'v eseen that done is something mounted on or in the chuck (which is not great if you have work in the chuck). If you have some pictorials that would be great.


No, Peter, I was not thinking correctly.  It has been some time since I used my TPG, and I simply did not remember what to do correctly.  I plead a senior moment, and will leave this thread alone before I post something dumber yet...  -Bob


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## petertha (Mar 15, 2020)

HaHa no worries Bob. I was looking forward to learning something new. I haven't used my TPG much & there aren't really a lot of Youtube or instructional references to using them like conventional turning, milling or surface grinding operations.

I've been doing some internal grinding. The results are pretty good, not spectacular but slowly getting better with a few tweaks here & there. My hunch is that there are a lot of variables with TP grinding - stock material, wheel type, tooling, feed & speed, grinder stability, lathe background vibration... I wish I could see some more examples as a point of reference. 

Next step is some home made arbors that I hope to make stiffer that ones I have. Themac has a funky taper unique to themselves for the tooling shank that goes into the mating spindle socket. I tried making a few test blanks by DTI-ing off the ones I have just using the compound. The fit is getting better but still not there. I may have to use the TS offset method (using a boring head). Once I have the dimensional taper recipe I'll be able to make some cool tools.

Pic of cast iron cylinder liner 0.0005" lapped #800 off after ID grinding.


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## petertha (Mar 15, 2020)

The other thing I should have mentioned is that the base of the dressing tool buts up against the lathe bed rail. So theoretically that is a repeatable position of the dressing point & therefore the grinding wheel relative to spindle center plane. Even though the wheel is getting smaller by dressing, the contact tangent should be a somewhat repeatable if I reset my DRO.

In reality I found ID grinding to be a bit weird. Its kind of like boring where you have to take the equivalent of a spring pass. But after measuring the bore progression vs carriage in-feed, there is still a bit of dimensional drift. My feed measurement is pretty good, I have a tenths indicator hard mounted to the table. But maybe the wheel OD is eroding a bit as I'm grinding, so its not like a single point cutter that essentially stays the same. The best strategy seems to be creep up on it thou by thou & measure every time. I'm happy with the dimensions but wish the surface finish was a bit better.


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## ddickey (Mar 16, 2020)




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## rgray (Mar 16, 2020)

My feeling of tool post grinders is they are a little like trying to use a drill press as a milling machine. Maybe not quite that bad.
But not a great way to get good results grinding.


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## petertha (Mar 22, 2020)

Not sure I agree. Like many things, it might be a function of who is using it, how its set up & multitude of other factors that go into precision machining. Have a look at this post. The TPG gets utilized on quite a few operations where the tolerances & finish is pretty demanding by most standards. Granted its not exactly a stock lathe after some of his mods, but I think in principle its a useful accessory. I'm just beginning my journey but something to aspire to.





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## mikey (Mar 22, 2020)

I've wanted a TPG for a long time but I cannot convince myself that I could clean up every single particle of grinding dust that will get on my lathe, even if I covered it up. Maybe I'm just paranoid but yeah, I can't bring myself to do it. If I ever find a beater lathe then I might set that up for a TPG.


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## rgray (Mar 22, 2020)

petertha said:


> The TPG gets utilized on quite a few operations where the tolerances & finish is pretty demanding by most standards.





mikey said:


> If I ever find a beater lathe then I might set that up for a TPG.




I just don't put it in words real well.

Yes they can be very accurate. But after using one on my lathe I really don't like the mess.
Better than a beater lathe would be an old cylindrical grinder with the internal grinding attachment.
I bought an old cylindrical grinder for $500 and though it's old it's still very accurate. 
Unfortunately it did not have the internal grinding attachment.
So I'm always on the lookout for another to complement this one or possibly replace it.

And I do have 2 tool post grinders. One is set up on an old lathe duplicator bed and grinds tapered stock up to 3 ft or so with 
the duplicator off settable tailstocks.


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## petertha (Mar 22, 2020)

I was concerned by the mess too, meaning fine abrasive dust & getting under the carriage wipers. First I wipe off the way oil between head stock & carriage just as a precaution. Not bone dry but not glistening wet. Then I lay down some old terry towel face cloths accordion style across the bed ways so they don't overhang much to interfere with the rotating lead screw / power feed shaft. On relatively short travel jobs its easy to just use a t-shirt material with small magnet on either end to hold it in position. Then to remove just fold it into itself, vacuum & remember which side is up to replace. If its white is shows any fine debris quite well. I also put a bit of rag stuffing in the chuck just behind the part so dust cant migrate into the chuck mechanism or into the spindle.

In my case (model 4-stroke cylinder liner) there was only about 0.004" (internal diameter) to remove so not really a lot of material. I was more concerned by abrasive material coming off the wheel dressing operation. The wheel is only 0.75" diameter & I held a vacuum up to it. Do what you can to keep things clean. Now if you have a bigger wheel like a 3-4" doing OD grinding, everything grows proportionately. Much more  wheel to dress, more part material to grind. I agree, a dedicated lathe or better yet cylindrical grinding lathe would be nice. Unfortunately with a regular lathe the spindle & tooling all have to be decently accurate & tight so its not like any junker would do. I've thought about a dedicated mini setup like using a knock-off Asian lathe especially for small parts & dedicated spindle motor, but I don't do enough of this to warrant the expense. In hindsight I think regular machining of (in this case cast iron) has the potential for as much or more damaging mess. I do essentially the same rag procedure with CI to keep the swarf & dust off the ways.

There is also a lot you can do with lapping (and often its required after grinding anyways). But its a messy, time consuming ritual & also requires specialized tools. Lapping anything more than 1-2 thou is getting into the inefficient range.


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## rgray (Mar 22, 2020)

Being a mechanic when I think cylinder I think bore and hone.
Now that's a small cylinder, but there is still a way to hone it. 
Prime candidate for the Sunnen hone machine. 
I have 2 of these old red ones, like this, minus the fancy gauge unfortunately.


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## petertha (Mar 22, 2020)

That is indeed the weapon of choice!. I'm envious! Pretty sure that's how all commercial RC engines are done, especially being hard chromed or similar coating. I perused some Sunnen manuals & tooling a while back wishfully thinking maybe I could replicate the expanding arbor mechanism & somehow figure out the stroking manually. But those heads are not exactly trivial & I cant say as I understand the  adjustment procedure having only seen them on YouTube vids, never in real life. For example when you make a bore setting, do the stones operate under spring or hydraulic pressure until that setting is reached? Or does it increment X amount every certain number of strokes? Another mystery to me is on tapered liners like 2-strokers (as opposed to parallel bores). Are the stones somehow set at a preset angle & then stroked in the same way?


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## rgray (Mar 22, 2020)

petertha said:


> For example when you make a bore setting, do the stones operate under spring or hydraulic pressure until that setting is reached? Or does it increment X amount every certain number of strokes? Another mystery to me is on tapered liners like 2-strokers (as opposed to parallel bores). Are the stones somehow set at a preset angle & then stroked in the same way?



The stones are pushed out by a wedge that they are riding on at all times. The adjustment dial simply turns a threaded rod that pulls a leaver at the back with a rod that pushes the wedge farther under the stone to extend it and apply pressure to the cut.

Modern machines may be more automated. I've never been around one of the newer ones. The old red ones like I have do nothing but rotate when you step on the "go" peddle. All cutting action is done by the user turning the dial. It has .0001 increments.

I don't know anything about tapered 2 stroke liners. 
In a past life (1988-2006) I was an Arctic cat snowmobile, Kawasaki, Stihl, Husqvarna (bikes and chainsaw) dealer.
Lots of 2 strokes there. Never seen a tapered bore in one.


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## petertha (Mar 22, 2020)

Thanks for the info. Taper may be a 2-stroke RC (most commonly ring-less) engine thing. I'm on the opposite end of the spectrum, don't know much about the bigger stuff LOL. The link I provided in post#12 talks about how hes sets up using defined mandrels. He is a power guru & one of the principle guys behind a well known USA pylon race engine manufacturer.

I'm using Acro barrel lap for the last operation.


			Acro laps Barrel  Laps and Blind Hole Laps
		

I stopped the TPG operation at 0.0010 - 0.0005" undersized which I was initially apprehensive about because the finish didn't seem awesome to the naked eye but slowly improving on that front. Also its held in a 5C collet (as light as practical) but  figured it might relieve itself a bit. Anyways the last but comes off with the lapping tool. Ugh, messy & time consuming. The tapered screw expands the splined brass barrel slightly. Its very much a feel thing. Then you have to clean the liner spotless just to measure. I'm holding 0.0001" according to the dial. But I experienced an unexpected issue. The liner is heat shrunk in an aluminum cylinder & that is another consideration. The OD/ID interference needs to be accurate or the shrink can adversely affect the bore. This is my first rodeo. The next one will hopefully be a bit more straightforward.


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## rgray (Mar 23, 2020)

petertha said:


> The OD/ID interference needs to be accurate or the shrink can adversely affect the bore.



Defiantly finish your bore sizing after it is assembled in the cylinder.
If running rings a cross hatch pastern is usually wanted for ring seating. Will be shining like a mirror after lapping and then you need to scratch the heck out of it to get a cross hatch. Seems like a terrible thing to do but is normally done with a ball hone shooting for a 60 degree cross hatch if I remember right.
Modern molly rings seat/seal easily. Chrome rings were the problem child's in that area, back in the day!


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## rgray (Mar 23, 2020)

petertha said:


> . The link I provided in post#12 talks about how hes sets up using defined mandrels.



Wow that's a long thread. looked it over more. You must mean post 121 ? I searched for what you were referencing but didn't find it on post 12.
In 121 he's talking about the taper on a piston. All pistons are tapered as the top expands with heat and grows.


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## petertha (Mar 23, 2020)

Sorry for any confusion. I referenced the ModelEngineMaker link in post #12 of this Hobby Machinist thread. Anyways in that MEM reply #121 he says 
_The piston's circumference at it's top is tapered for use in *tapered cylinders*.  _

more info page 27 this link








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general info





						Tapered-Bore Engine Break-in - Upgraded - RCU Forums
					

Glow Engines - Tapered-Bore Engine Break-in - Upgraded - This issue is revisited time and time again by many modelers. Every week, or two, another modeler opens a new thread, asking questions about this subject. I have referred many of them to the original thread. Since the original thread was...



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I'm not an 2-stroke engine designer & my experience is limited to RC (methanol burning, glow plug ignition, quasi-dieseling) stuff which may operate at different principles & rpms to larger displacement engines. I've heard of different permutations in RC depending on applications: tapered liner + tapered piston, tapered liner & cylindrical piston. Supposedly part of the pinch point magic is the piston effectively molds into a resultant slight barrel shape during break in. But even if they replicate the shape to begin with, it doesn't work. I'm sure there is a wealth of knowledge out there. Heck, if I still had the engines I would just measure them LOL.


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## rgray (Mar 24, 2020)

petertha said:


> Sorry for any confusion. I referenced the ModelEngineMaker link in post #12 of this Hobby Machinist thread. Anyways in that MEM reply #121 he says
> _The piston's circumference at it's top is tapered for use in *tapered cylinders*._



Yep ...I missed that. Guess I should have put more powerful readers on. lol  The type is small on that site.
The propwash info shows honing on a sunnen hone machine.  Truing sleeves are used to "square" the hone abrasive square and flat.
Maybe they make their own truing sleeve with the taper to true the stone in a taper. Interesting stuff.


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## petertha (Mar 25, 2020)

I've wondered about that. Do the Sunnen cutting stones get dressed so the corners do the cutting until they wear down a bit on the bore? 

I've visualized different ways to make an expanding arbor & even found some skinny abrasive stones sticks. But the real trick is the micro wedge adjustment to on the fly to incrementally increase the cutting diameter. I guess that's why they developed Sunnen's to begin with.


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## rgray (Mar 25, 2020)

Dressing the stones is is done with a hardened truing sleeve so they are dressed rounded.
Just one stone per mandrel. Or stones on one side maybe I should say.
There are many variations of stones when getting into larger and longer mandrels.
Two stones lengthwise for longer mandrels is common. Some larger ones have 4 stones length wise, but they are 2 holders 
that are wider with 2 stones per holder with some separation between them.
cheaper mandrels are sacrificial, more expensive have replaceable wear pads on the opposite side of the stones, they are usually brass.
A honing oil pump runs anytime the mandrel turns so constant oil flow on the part is normal.


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## petertha (Mar 25, 2020)

I might have been looking at Sunnen portable honing heads at the time thinking they might lend themselves to remote power (lathe) operation. But I still don't have a clear picture of the head components & adjustment process. More research required.


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