How long is a Jarno dead center?

The real Leigh · May 20, 2008

Hi All,

I just got a #12 Jarno dead center, and it sticks out 3 1/2" from the flat camlock face. This appears to be much farther than the photos I've seen. It extends so far that the dog clamp arms are too short to mount a workpiece properly.

The spindle bore and taper are clean and unobstructed. I just ran a bronze wire brush through the spindle to be sure. The center appears to seat properly in the taper.

This is a high-quality US-made product, not a piece of chicom junk.

I don't understand why it's so long (9" OAL).

Any comments or suggestions would be most welcome.

Thanks.

- Leigh

macona · May 20, 2008

I had the same experience you did. Picked up a cheap J12 center off ebay and the thing stuck out a mile. Used carbide and machined it down and now I am happy.

I think the taper in the EE is slightly smaller than what would be speced for J12. Thats why they use the J12 to MT2 adapter.

Cal Haines · May 20, 2008

The J12 to MT2 adapter is shown in parts picture E-10 of the 1942 10EE manual that is available online at metalillness. It's part #5, page 23 of the .PDF file. It's 3" long and 1-3/8" at the small end. IIRC, it doesn't stick out very far past the face of the spindle. (I'de check, but I have the drawbar for the collet close in place and it's sort of a pain to remove.)

link to manuals:
http://bbssystem.com/viewtopic.php?t=1507

Cal

The real Leigh · May 20, 2008

macona said:
I had the same experience you did.

OK. So I'm not crazy after all (well, maybe not). :crazy:

I have access to a very good precision cylindrical grinder, and a guy who knows how to use it properly. I might turn this one down. Seems a shame to obliterate the manufacturer markings and such.

I could also leave the taper intact and turn down the point, but that's a lot of metal to grind off. It would probably destroy the carbide tip due to the amount removed.

Thanks much.

- Leigh

The real Leigh · May 20, 2008

Cal Haines said:
The J12 to MT2 adapter is shown in parts picture E-10 of the 1942 10EE manual...

Hi Cal,

Perfect double

I'm familiar with the adapter, although I don't have one.

I might make a J12 to MT3 adapter, since I have an MT3 dead center. I see no obvious advantage in being able to interchange tooling between the headstock and tailstock, although perhaps I'm missing something. :confused:

I do have a very nice MT2 live center for the tailstock.

Thanks.

- Leigh

johnoder · May 20, 2008

Many centers made for grinding machines have extended noses, often cylindrical for the length of the extension.

By defintion, the tapered portion of a 12 jarno is 6" long.

(big end 12/8ths, little end 12/10ths and length 12/2 )

John

The real Leigh · May 20, 2008

Hi John,

This one is tapered uniformly (0.050"/inch) up to where it joins the 60º point taper.

It matches all the nominal dimensions of the #12, except it keeps getting bigger. I suppose it depends on how you define "end".

Thanks.

- Leigh

Cal Haines · May 20, 2008

johnoder said:
...
(big end 12/8ths, little end 12/10ths and length 12/2 )

Interesting. The small end of my adapter is 1.37", measured where the fillet on the end starts. I don't know if mine is real Sydenium, or shop made. Anybody else got one handy?

Cal

johnoder · May 20, 2008

As you can see, referriing to it as a Jarno 12, by Monarch or whoever, is only partially true.

Plainly, their sleeve style adaptors were not six inches long. It made sense to whack them off at 1.37 diameter on the small end, as I expect that is somewhere near spindle bore.

I suppose the partially true includes the 1.500 dia. big end and the .6" taper per foot.

John

sparkness · May 20, 2008

It seems that many lathe mfg's have thier own version of tapers I have a sheldon and the headstock uses the mt5 taper but only a portion, some have called a short mt5 but thier is no standard.

The real Leigh · May 20, 2008

johnoder said:
Plainly, their sleeve style adaptors were not six inches long. It made sense to whack them off at 1.37 diameter on the small end, as I expect that is somewhere near spindle bore.

Hi John,

Given that the nominal ID of the spindle is 1.40625", it makes little sense to provide the portion of an accessory significantly smaller than that. The Jarno 12 is (small/large) 1.2000/1.5000 x 6", while the 13 is 1.3000/1.6250 x 6.5".

The next smaller size (11) is 1.1000/1.3750 x 5.5" which would slide all the way through the spindle. So it appears they picked the smallest one that was larger than the spindle ID.

I think the taper per foot(inch) was the important characteristics.

- Leigh

naumanng · May 21, 2008

Hey ya'll,
I have been lurking (learning) on this forum for some time. Ya'll have been a great help with my 1941 EE! Thanks to all! Leigh, John Oder is correct, the EE spindle taper is not technically a Jarno taper, it is only a portion of a Jarno taper. This portion is included in the #12,#13, and the #14 Jarno taper. As you have already found out, these Jarno taper dead centers are HUGE and way too long. Like Macona, I found a brand new Royal #13 Jarno dead center on ebay for $8.00 plus shipping, stuck it in my EE's spindle,smacked it with a piece of hardwood and turned it down compatable with the drive plate. Wa La! One piece dead center. Cost $18.00 plus one half hour machine time.
Satisfaction in making it myself-priceless. Leigh, I don't believe you should worry about having a carbide dead center in a headstock center. JMHO. Your situation may be different from mine.
From the center of the machining universe,
George

The real Leigh · May 21, 2008

naumanng said:
John Oder is correct, the EE spindle taper is not technically a Jarno taper, it is only a portion of a Jarno taper.

Hi George,

I'm afraid it is a Jarno taper, as determined by the .050"/inch taper. It just is not a particular defined size Jarno taper. The Jarno spec is relatively unique in the world of tapers in that the taper angle is identical for all sizes. Thus you could construct a #12.5 or a #4.75 or whatever you want.

naumanng said:
Leigh, I don't believe you should worry about having a carbide dead center in a headstock center.

True enough. Since it's only a weight-bearing point and the work does not rotate on the center, the carbide is of no particular value. I just hate to ruin a nice piece. I haven't checked the hardness yet. I can probably bandsaw a couple of inches off and turn a new point.

And I lied earlier...
This center does grow out to 1.5000" as it should, then changes to a cylinder which extends to the point taper. I didn't realize that.

Thanks.

- Leigh

naumanng · May 21, 2008

Hey Leigh,
I am just hung up on the fact that a Jarno taper has a certain length spec'ed for each taper number. The good news is that there are plenty of these large taper centers around. Great "stock" for all of us to utilize. So shed a tear if you must, then chop the tip off and have fun!
George

Cal Haines · May 21, 2008

naumanng said:
Hey ya'll,
I have been lurking (learning) on this forum for some time. Ya'll have been a great help with my 1941 EE! ...

From the center of the machining universe,
George

Welcome George!

Good to see another round-dial owner show up at the party. I have s/n 24315, built 11-1943. Would you mind sharing your s/n and build date? (I've been trying to assemble a better list of the serial numbers vs year.) Does your machine have an MG drive?

Cal

The real Leigh · May 21, 2008

Cal Haines said:
I've been trying to assemble a better list of the serial numbers vs year.

Hi Cal,

Is there something wrong with this one?

It shows the last s/n for each year. I believe it came from Monarch.

- Leigh

The real Leigh · May 21, 2008

naumanng said:
I am just hung up on the fact that a Jarno taper has a certain length spec'ed for each taper number.

Hi George,

Not exactly.

All of the dimensions (in inches) are calculated from the desired size. Given a number (size) N:
the small end diameter is N/10;
the large end diameter is N/8;
and the overall length is N/2.

Although N is an integer by convention and in published tables, the formulas could be applied to any value.

Ref: Standard Tapers in Machinery's Handbook (page 926 of the 24th ed.)

- Leigh

Cal Haines · May 21, 2008

The real Leigh said:
Hi Cal,

Is there something wrong with this one?

...

It shows the last s/n for each year. I believe it came from Monarch.

- Leigh

I don't know what the source of the list is, but it apparently was not Monarcy. It has a lot of problems in the round-dial years.

John, who worked at Monarch (during the 1990's ?) posted this:

jlegge said:
Peter, if the serial number book you have is the same one I saw a number of years ago I would only take what it says with a grain of salt. The serial numbers for Monarch were so full of errors to the point of being close to useless. I wish I could remember the name of the book. The chief engineer of Monarch at the time show it to me, and pointed out many of the errors, while we where discussing other matters.

Monarch start using serial number for their lathe in 1927 starting with 1000, and number machine in the order that they where placed in the build schedule. The sometimes prefixed the serial numbers so they would know what type of lathe it was without having to look up the number all the time.

John

see also: http://www.practicalmachinist.com/vb/showthread.php?t=100498

Cal

The real Leigh · May 21, 2008

Cal Haines said:
I don't know what the source of the list is, but it apparently was not Monarcy. It has a lot of problems in the round-dial years.

Hi Cal,

John also posted in that thread:

jlegge said:
Monarch start putting serial numbers on their lathes in 1927 starting with SN-1000. Every machine Monarch made thereafter was given the next number available (or assigned to it).
Monarch did not assign serial number per series of lathe. Their numbers was sequential over all the machines they built. There was nothing special with the number and no special coding. It was just the a number assigned to a machine when that machine was ordered for production.

This points up two errors in the interpretation of the aforementioned table:

1) The numbers shown in the table are the last number for a given year, not the first, as evidenced by John's 1927 s/n 1000 statement. The table shows s/n 1410 for 1927, indicating that 411 lathes were ordered that year, numbered 1000 through 1410.

2) The serial number was assigned when the production order was entered, but the date was presumably stamped on the s/n plate when the lathe was completed. All of the discrepancies discussed are of lathes with dates in the year following the one shown in the table. This would be expected for machines which were ordered in one year and shipped the next.

- Leigh

Cal Haines · May 21, 2008

list of Monarch serial numbers vs. year

The table may, in fact, correlate to the year a machine was ordered. However, the more common question is when was a particular machine built.

It would be nice to know the true source of the table, based on John's comment.

Cal

How long is a Jarno dead center?

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