# Jacobs tapers



## gunboatbay (Sep 10, 2011)

I have a Sieg SX3 mill and a Sieg C6 lathe, neither one of which is a very robust machine, but satisfy my needs. I am not happy with the drill chucks on either machine, so I'm going to buy one quality 1/16-1/2 chuck for use on both machines. I would like to hear the pros and cons of the various sizes of Jacobs tapers available for the chuck adapter. It seems that the JT 3, 6 or 33 would suffice, *but which one ??*.


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## kvom (Sep 10, 2011)

I'd select the chuck you need and then get the arbor it takes. Does your mill spindle and lathe tailstock have the same taper?


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## 90LX_Notch (Sep 10, 2011)

JT33 is has been known for it's inability to hold, that's why they came up with a threaded safety ring for it.


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## pete (Sep 10, 2011)

Gunboatbay,
I'm assuming both your mill and tailstock are MT 3? If so then check out Glacern Machine Tools integral shank keyless drill chucks. I also own an Albrecht and they compare pretty well at close to 1/3rd the price.

Pete


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## Omnimill (Sep 10, 2011)

My best chuck is a Albrecht and that has a "B16" (metric) Taper!

Vic.


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## gunboatbay (Sep 10, 2011)

I should have mentioned; the mill has an R8 spindle and the lathe an MT3, so I'll need two chuck adapters. As far as buying the chuck of my choice the getting adapters to match it, that's my plan. The reason I asked the original question is that Enco seems to have about the best prices on Albrechts and the're available with just about any Jacobs taper, so I thought someone could steer me in the right direction. The comment about the JT33 is welcome, so I'll take that one off my list. Leaving me to decide between the JT3 and JT6. Comments anyone??


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## pete (Sep 10, 2011)

OK, Reading your first post it could be taken two ways, One, You want to buy one chuck and two arbours. That won't work. Or you meant you want to buy two arbours and two quality chucks. By the way, Your C-6 is MT 2 not MT 3. I own one.

Pete


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## MachineTom (Sep 10, 2011)

I assume you are buying Two of the same chucks, The JT6 is the largest so go with that . Why, any of the smaller tapers 33, 3, have a smaller cross section a the the junction of the chuck taper and the machine taper, smaller leads to mor flexing, not something you want when drilling. The intergrao shanks are THE best shank of all, and the premium is small, If you bend an Intergral shank chuck, most machines would be trashed. 

If you think one chuck with 2 arbors lose that idea quick. To prevent seperation of arbor and chuck, clean bore, with brake clean, spirits, whatever will clean without leaving a film, warm the top of the chuck with a heat gun, put locktite on the arbor, then slam the abor end down on a anvil, or large hammer, to set the chuck, now its time to use it. The last thing you ever want is the chuck to come loose from the arbor. I'd suggest that if your lathe is large enough to have an MT-3 taper, buy a 5/8" Albrecht, a interesting point is a Albrecht 5/8 intergral shank chuck is shorter in installed lenght than a 1/2" with a arbor. If you have ever used a S&D drill bit in a 1/2 chuck and had to use a strap wrench to loosen the chuck, that is why I replaced the 1/2 chucks with 5/8" .

Your mileage may vary.


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## Stan (Sep 14, 2011)

I don't want to be picky but a JT3 is bigger than a JT6
Large end diameter of JT3 is .8110 and a JT6 is .6760
A JT33 is .6240


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## MachineTom (Sep 15, 2011)

You are correct, it should have been a #2 instead of a 3. Albrecht/other 1/2" chucks don't come in# 3 mount, #6 is the largest arbor for a 1/2" chuck, at least what I could find.


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## Swede (Sep 16, 2011)

I'll second the keyless chuck in the Albrecht pattern, they are SUPERB chucks. Albrechts themselves are expensive, but the clones seem very nice at a great price. I bought an SPI Albrecht clone for maybe $75 a couple of years ago, and my finest gauges showed no differences between the clone and a real Albrecht.

One huge word of caution - Used Albrecht chucks can be found on eBay at good prices, _but always be sure there are close-up photos of the chuck jaws._ The body or mechanism rarely fails, but _the jaws themselves can get trashed by careless use._ Don't ever bid on a chuck with unknown jaws.

The jaws can be replaced, but with a bit of care, you can avoid that. If in doubt, go for a new Albrecht clone.

One final thought - I've heard of guys who buy a $200 Albrecht and then mount it onto a $5 Chinese arbor. All of the precision in that chuck is probably gone. A few years back, I was curious and measured the runout on some Chinese chuck arbors I had kicking about, and (for me, at least) they were terrible. I'll never buy a Chinese arbor again. It's odd that the clone chucks themselves are often excellent, but the arbors are not. Go figure. YMMV.


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## Lakc (Sep 16, 2011)

Swede  said:
			
		

> One final thought - I've heard of guys who buy a $200 Albrecht and then mount it onto a $5 Chinese arbor. All of the precision in that chuck is probably gone. A few years back, I was curious and measured the runout on some Chinese chuck arbors I had kicking about, and (for me, at least) they were terrible. I'll never buy a Chinese arbor again. It's odd that the clone chucks themselves are often excellent, but the arbors are not. Go figure. YMMV.


An expensive genuine Jacobs R8/JT6 arbor only lists as .003 runout, so by the numbers, everyones mileage varies too much.... I measured about .0015 on the Indian version I eventually bought.


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## Swede (Sep 20, 2011)

Lakc  said:
			
		

> An expensive genuine Jacobs R8/JT6 arbor only lists as .003 runout, so by the numbers, everyones mileage varies too much.... I measured about .0015 on the Indian version I eventually bought.



I don't disagree. I don't mean to slam import tooling, and it has gotten a lot better in the last decade. I guess I simply wanted to warn against pairing a known high-precision chuck to a suspect arbor.

Actually, I'm surprised at your numbers. A good arbor, when mounted in a quality spindle, should have a TIR of far below 0.001"... I'd want to see better than 0.000,2 inches. I assume you are talking mm with those values?


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## Lakc (Sep 20, 2011)

No, that's in inches. I didn't spend a whole lot of time setting up the measurement, cleaning the spindle recess, etc. 
My main point was my utter amazement at the stated Jacobs tolerances.


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## Swede (Sep 23, 2011)

Wow, if Jacobs is saying the tolerance is 0.003", that may as well be +/- 0.100" as far as I'm concerned. That's unacceptable. I'm not sure where they are going with that. 0.003" at the jacob's taper surface can turn into 0.015" or worse at the drill tip.

Just for fun, I checked a Chinese R8 --> JT in my mill and it was less than 0.0001" at the middle of the taper. I guess in the end, check 'em out before jamming on a new Albrecht.


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## 10K Pete (Sep 24, 2011)

I'd like to add my experience here. I never just mount a chuck to an
arbor right out of the box(s).

Clean the quill taper and make sure it's in perfect condition. Clean the adaptor and make sure it's in perfect condition. Put the adaptor
in the quill and tap in gently in with a soft hammer. Mount an indicator and check the runout of the chuck end of the adaptor. Mark the
high side with a felt pen. Remove the adaptor, rotate it in the quill to
a different place then tap it in again. Check the runout again. Repeat
until you have minimum runout.

Clean and inspect the chuck taper, then gently mount it on the adaptor in the quill. Chuck a ground dowel pin, like 3/8", in the chuck and tighten gently. Check the runout. Move the chuck around
on the adaptor until you have zero runout. Yes, you will find a place. If you don't then get another chuck or adaptor!!

When you have the chuck/arbor assembly running true, then tap the adaptor into the chuck.

When the chuck and adaptor tapers fit properly you don't have to use Loctite or a big hammer.

My two cents...

Pete


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## Lakc (Sep 24, 2011)

Probably quite correct Pete!

My reaction was more like "OMG I finally pried open my wallet for a new toy, lets play"! :-[


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## dalem9 (Sep 24, 2011)

All make sense to me .Good advice .Thanks Dale


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