How much nmtb arbor/spindle contact is enough?

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I used hi-spot blue to check how much contact I had after taper-grinding the arbor on the vintage B&S no. 1 univ. grinder. I had to grind it as the former owner had somehow chowdered one side of the arbor-looked like coarse sandpaper and I didn’t want it in my spindles. I set up the grinder as best as I could with dial indicators and the built-in taper scale, which ends at 3 in./ft. The 50-taper arbor is 3.5 in./ft. So some interpolation was needed. Anyway as you can see only the bottom inch of the arbor taper contacted the spindle. Is that enough or do I have to regrinding it. Drawbar was drawn up tight after blue put on.

Cannonmn said:

See photos

John Morris has shared 2 photos with you! | Flickr

I used hi-spot blue to check how much contact I had after taper-grinding the arbor on the vintage B&S no. 1 univ. grinder. I had to grind it as the former owner had somehow chowdered one side of the arbor-looked like coarse sandpaper and I didn’t want it in my spindles. I set up the grinder as best as I could with dial indicators and the built-in taper scale, which ends at 3 in./ft. The 50-taper arbor is 3.5 in./ft. So some interpolation was needed. Anyway as you can see only the bottom inch of the arbor taper contacted the spindle. Is that enough or do I have to regrinding it. Drawbar was drawn up tight after blue put on.

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Half the issue is all you are working on?

"Looks as if".. the FEMALE taper has suffered some front / "big" end wallowing.

As can happen, over time.

D'you have a means of confirming or denying if that is the case?

"Something" seems to be in need of further grinding work. Not "impossible" it is no longer the toolholder.

Best to ascertain WHICH before doing any more grinding?

Spindle shows wallowing? Optical illusion, difficult photo-taking conditions, lousy angle. Looks quite round in person.

None of the pre-grinding arbor surface Remains, I took off quite a bit all over. One further bit of info-the arbor seated in the spindle with a distance of about 1/8 in. Between spindle face and arbor flange, meaning very little of the flange end was ground. A lot of the top (drawbar) end was ground. The arbor had nothing to do with any of my machines, came firmly attached to a boring head from Eboo. Separate thread relates the saga of separating boring head from arbor.

Cannonmn said:

Spindle shows wallowing? Optical illusion, difficult photo-taking conditions, lousy angle. Looks quite round in person.

None of the pre-grinding arbor surface Remains, I took off quite a bit all over. One further bit of info-the arbor seated in the spindle with a distance of about 1/8 in. Between spindle face and arbor flange, meaning very little of the flange end was ground. A lot of the top (drawbar) end was ground. The arbor had nothing to do with any of my machines, came firmly attached to a boring head from Eboo. Separate thread relates the saga of separating boring head from arbor.

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I followed that other thread. But.. different thread or threads ISTR you have a goodly collection of OTHER "store bought" 50 Taper goods besides this critter?

I would expect bluing-up more than just one or two of the others could tell you more about the spindle's taper condition?

If in good health and OTHERS blue to full-bearing, then it can become your "reference" for bumping the grinder angle an RCH or so and finishing this one to proper fit.

If the spindle taper is NOT in good condition, you should make it so, first.

A poor fit - of either - just aggravates any "beating" or fretting effects and accelerates wear.

i think you ground away too much at the top of the spindle. also i like to do this with less blue.

dian said:

i think you ground away too much at the top of the spindle. also i like to do this with less blue.

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Point. One must.

Otherwise all yer determining is how much blue can be stashed in some other container than what it came in!

there was a video from Big Kaiser about checking the fit of their big plus spindles, and they used a bead (3 or 4 beads actually) of the blue axially on the taper, not wipe on, but a narrow bead, and if the fit was like it was supposed to be, then upon removing the tool the spread of the blue was the indicator of the fit - perfect fit = very even color (thickness of the blue) all over the mating surfaces, no "fat" dark spots where the beads were

doing it the usual way of applying very thin even coat on one of the tapers and checking the print on the other, you'll get smearing where the surfaces met before the tool was pulled in all the way and so on, not to mention that it isn't easy to have a perfect spread of the blue on the female taper - and you need to, because that is what the method relies on to judge the print correctly

and the spread of the blue on the female taper in the OP pics seems quite uneven, so I wouldn't trust the print all that much

here is a pic of prints I took on my universal mill, print on the left is from the horizontal spindle taper which hasn't seen any use at all, so the taper is in like new condition, and the other print is from the vertical head spindle taper - not nearly as good - both prints were made using the "correct" method of spreading the blue on the taper as evenly as I could - switched to slowest speed and used lint free wipes to get even coverage

jz79 said:

..the spread of the blue was the indicator of the fit - perfect fit = very even color (thickness of the blue) all over the mating surfaces, no "fat" dark spots where the beads were
.
.
...
and the other print is from the vertical head spindle taper - not nearly as good - View attachment 302220

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Even so, there is contact at "enough' points or bands to call it better than what he is so far getting.

Nowhere close to the correct taper angle - right now you have only a very small amount of contact at the large end of taper, but it's impossible to tell exactly how much because of the excessive amounts of blue.

Alternatively, you may have removed so much material that you now have face contact instead of taper contact, although that is impossible to determine from the photos.

In either case, if that holder is not scrapped already, it will be by the time you have corrected the taper....

Next time indicate in the taper from a known good holder or a gauge taper and forget about the scale.

Also, since you have the taper ground too obtuse and actually have more than just a line around the base, it's a good indication that your spindle taper is bell mouthed a bit as Thermite suggested, however once again that may be just the excessive amount of blue giving a false impression.

Thx for all the info, new area for me. I do have one new holder given to me by the mill seller in MA, who also makes the holders and other stuff, their plant has a long aisle with Cincy horizontal dial mills either side, each with a dividing head and operator, cranking out gears. Yes I have lots of other holders so I’ll save this new one as a setup/spindle-check gauge. I did see thick sparking from narrow end and little sparking from wide end while grinding, and tried to compensate with crankology buy obviously failed. Had no idea how to get blue on evenly so used narrow paintbrush, thus the streaks. Will follow methods described above in future. Wondering if anyone has successfully built up an overground or worn nmtb-type holder? If comment about scrap wasn’t there Id certainly be back at the grinder trying to skim a bit more off the wide end. The nmtb50’s with 2 1/4-10 thread are priced like gold on new retail, and just don’t seem to show up at all on the used market. Cheaper to buy a beat-up tool with the threaded arbor attached, which I’ve done because as I’ve learned the arbors can be screwed in so tight they have to be cut out. So I can almost see myself epoxying pieces of shim stock ribbon to the overground part. That picture will probably give Thermie a coronary, so remember it is only a fleeting image, don’t think I’ll really try that unless I’m told it is an accepted practice. This arbor is only for an older Criterion boring head, and will only be in one particular non-DRO-equipped mill that is set aside for boring.

Cannonmn said:

Thx for all the info, new area for me. I do have one new holder given to me by the mill seller in MA, who also makes the holders and other stuff, their plant has a long aisle with Cincy horizontal dial mills either side, each with a dividing head and operator, cranking out gears. Yes I have lots of other holders so I’ll save this new one as a setup/spindle-check gauge. I did see thick sparking from narrow end and little sparking from wide end while grinding, and tried to compensate with crankology buy obviously failed. Had no idea how to get blue on evenly so used narrow paintbrush, thus the streaks. Will follow methods described above in future. Wondering if anyone has successfully built up an overground or worn nmtb-type holder? If comment about scrap wasn’t there Id certainly be back at the grinder trying to skim a bit more off the wide end. The nmtb50’s with 2 1/4-10 thread are priced like gold on new retail, and just don’t seem to show up at all on the used market. Cheaper to buy a beat-up tool with the threaded arbor attached, which I’ve done because as I’ve learned the arbors can be screwed in so tight they have to be cut out. So I can almost see myself epoxying pieces of shim stock ribbon to the overground part. That picture will probably give Thermie a coronary, so remember it is only a fleeting image, don’t think I’ll really try that unless I’m told it is an accepted practice. This arbor is only for an older Criterion boring head, and will only be in one particular non-DRO-equipped mill that is set aside for boring.

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When I said scrapped, it was.because if you remove too much material from the taper the overall geometry will be altered to the point that it will not fit in the spindle - it will contact the face before the taper, or the drawbar boss at the top will protrude too far etc.

I'm sure for your purposes it could be salvaged after correcting the taper by grinding the face and the drawbar boss back to the correct distance from the gauge line on the taper. No need to mess around with buildup or shimming.

Ok gauge line def, found one but still not crystal clear, there must be an agreed-upon convention wrto these arbors?

“ Gage Line - A defined line, intersecting and perpendicular to the spindle axis, from which the tip of a tool is measured. The line may be defined from a point on the spindle itself or on a tool holder, provided all tool holders have the same mechanical construction. For setting up tools, it is often more convenient to measure the tip of the tool at a remote location and thus measure from a tool holder reference line or point.”

Cannonmn said:

Ok gauge line def, found one but still not crystal clear, there must be an agreed-upon convention wrto these arbors?

“ Gage Line - A defined line, intersecting and perpendicular to the spindle axis, from which the tip of a tool is measured. The line may be defined from a point on the spindle itself or on a tool holder, provided all tool holders have the same mechanical construction. For setting up tools, it is often more convenient to measure the tip of the tool at a remote location and thus measure from a tool holder reference line or point.”

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True, and important to CNC with tool-changers and magazines, tools pre-set over on a bench using a fixture plus-plus.

Less crucial in all-manual, where you are more likely to be directly involved, and setting the tool with the machine itself as "holder".etc.

But of GREATER importance- as already mentioned - is the grinding you've been doing that has very LIKELY already reached the point where you are seating on the flange before the taper can even fully engage. Or WILL do as you try for another correction?

There wasn't a lot of meat to spare. Using-up ANY of it affects the seated depth, and there goes the useful side of a known gage line, all holders, same race and tribe.

The reality is that holders - cheap or not - are "consumables". Need repair? Put them on ebay and buy new. Many is the "revenue" shop as can't generally risk f**ked-up product over mixed, odd-ball holders that take extra effort to "normalize" said extra effort not assured to be remembered every go.

Annnnnd ...

Even if you are cycling ten holders and each gets only one-tenth the total wear, there is but ONE spindle-taper that has to eat ALL ten in turn.

So it is the harder-working spindle that is - generally - "harder", and that we at least strive to protected for as long as possible.

WHEN the spindle IS reground, the flange may need adjusted as well.

You can only do this a limited number of times, yah?
And with utmost care, of course.

That work is well-worth engaging a specialist. Really. It is.

A good one who does this every day as "Day Job", will add YEARS to the life of a(ny) marginal spindle. You won't generally need it done twice.

"The reality is that holders - cheap or not - are "consumables"."

The troll is post pooping like crazy today!

“But of GREATER importance- as already mentioned - is the grinding you've been doing that has very LIKELY already reached the point where you are seating on the flange before the taper can even fully engage. “

There’s about 1/8 inch of shiny taper visible above the flange, when drawbar is tight. So I guess not all the “grindability” is used up yet.

I still need someone to explain where the accepted gauge line is on these holders.

Cannonmn said:

“But of GREATER importance- as already mentioned - is the grinding you've been doing that has very LIKELY already reached the point where you are seating on the flange before the taper can even fully engage. “

There’s about 1/8 inch of shiny taper visible above the flange, when drawbar is tight. So I guess not all the “grindability” is used up yet.

I still need someone to explain where the accepted gauge line is on these holders.

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I thot' you had found that?

That is "published" info as part of the spec, one of the dif's between NMTB, CAT (not hard to rig to use either), and metric-based "BT" which is still possible, but needs a touch more work to prep to use if you must mix.

MIND "all manual", drawbar, and frugal-budget again.

Yah do NOT want to mix 'em in a toolchanger and pull-stud environment!

The scarcity of these nmtb50:arbors with 2 1/4-10:threads suggests a little project, taking my otherwise useless nmtb50/1.5 in. Weldon holder

John Morris has shared 3 photos with you! | Flickr

and making 2 1/4 in. threaded/Weldon adapter for it. I have no 1.5 in. Weldon tooling, neither does Eboo.

Cannonmn said:

The scarcity of these nmtb50:arbors with 2 1/4-10:threads suggests a little project, taking my otherwise useless nmtb50/1.5 in. Weldon holder

John Morris has shared 3 photos with you! | Flickr

and making 2 1/4 in. threaded/Weldon adapter for it. I have no 1.5 in. Weldon tooling, neither does Eboo.

Click to expand...

If this is for the Wallbanger, gage line doesn't matter, FIT surely does. Boring heads can put seriously assymetrical loading into their mounts and aren't worth spit if they can shift about.

Do whatever works best and fits snugly and repeatably, 'coz "repeatable" is a decent indication OF a sound fit.

"Do whatever works best and fits snugly and repeatably, 'coz "repeatable" is a decent indication OF a sound fit."

You are a troll, you know nothing of these things.

“I'm sure for your purposes it could be salvaged after correcting the taper by grinding the face and the drawbar boss back to the correct distance from the gauge line on the taper“

Where is the gauge line on the taper? Top of flange? At the “break” where the taper begins above the flange? That’s what I still don’t know.