Closed End Mandrel Runout...

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SuperDave

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... Do any of you using a closed end mandrel have to deal with run-out?

I bought one for a Statesman and tried to use my Jacobs Chuck and have too much run-out. Drill bits run straight and true. I have fiddled with it for waaaaay toooo long and cannot find a "sweet spot" (thinking that the two flats for the wrench might be the culprit) so, I am assuming that a collet is the best way to hold the bugger!:([}:)]
 
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jhs494

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Have you tried taking it out and replacing it at the same spot?
If the runout is the same amount at the same spot you could try placing a shim between the jacobs chuck jaw and the mandrel. This will shift the centerline over and eliminate some of the runout.
You will have to adjust the shim thickness until it runs true.

Mark the jacobs chuck jaw and the mandrel with a marker to keep the timing the same.
It may take a few attempts to find out where the shim needs to be unless by chance you have a dial indicator.

Just a thought.
 

SuperDave

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Originally posted by igran7

You may just have a bad one Dave. If you got it at A.S. I would call Bill and see what he says.

Joe,

Yeah, I got it from AZS. I was all pumped to go "cap-less" tonight but the run-out is easily 1/32"+ and worse on the far end.:(

If I try different locations by twisting the mandrel, it gets as bad as 1/4"! So, I was thinking that I would try a collet chuck (if I can find someone close by) just to see if I could isolate it to the mandrel or jacobs chuck. If it runs true in a collet, I can then assume the jacobs chuck is the issue (or a dirty taper) but that doesn't explain the drill bits running fine, the MT Buffer running true,...

Do you use a jacobs chuck or a collet? You have several mandrels, have you had any issues?

We are going to be in Clackamas Saturday afternoon, watching over some elderly parents for some friends, and I am hoping to stop by a machinist friends shop on the way to talk about custom components. I can talk to him about is as well.

Dave
 

igran7

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Dave, I use a Oneway Talon scroll chuck, I've never tried it with a Jacobs chuck. You mentioned that you were all pumped to go "cap-less" with a Statesman pen. Is this the Jr. version or the full size? If it is the full size and you are trying to go Cap-less that might be the problem. To my knowledge A.S. doesn't sell a mandrel for closed-end cap-end pens Statesman/Gentlemen, only closed-end. They do offer them for many of the other kits including the JR. Statesman. If you are trying to use the mandrel on the upper barrel, it may only be catching on a portion of the brass tube.

My son's birthday is this Sunday the 16th and we are heading to Madras or I'd have you stop by to test it on the scroll chuck.
 

SuperDave

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Joe,

I was being cute... I was meaning the end cap on the long barrel. I went back out and put the mandrel into the Jacobs chuck using the brass barrel end, firmly attached and and checked the run-out on the opposite end and got the same result. I then disassembled the mandrel and chucked it up without the center screw... same thing.

I will try your four-jaw approach tomorrow morning and see what I get. I have a friend in town with a collet and draw-bar, as well as a metal lathe, so I might try him as well. I am not fully convinced it is the mandrel. With the mandrel showing run-out regardless of which end is chucked into the Jacobs chuck, I am thinking it might be the chuck I am using.

Thanks for the offer, that was generous. Have a great time in Madras!
 

Randy_

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Originally posted by SuperDave

.....I am not fully convinced it is the mandrel. With the mandrel showing run-out regardless of which end is chucked into the Jacobs chuck, I am thinking it might be the chuck I am using.....

It is really hard to understand how the Jacobs chuck could be the problem if drill bits run true when used in the chuck??
 

gwilki

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Dave
I will be interested to hear how your experiment goes with either a collet chuck or a jaw chuck. I use collet all the time. You may well find that the problem using a Jacobs chuck is that they are not made to take lateral pressure. If you are getting run out without any pressure, than you can ignore my rambling. But, if it only comes in when you are turning, it may well be the jacobs chuck. They work fine for drilling, but when you start exerting any pressure at all against them laterally, they can't take it.
I'm sure that you have already looked at this, but make sure that the closed end mandrel that you are using is very snug in the tube with no pressure being applied by the nut. It may be that the mandrel is too small and not centering in the tube.
 

SuperDave

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I visited a friend that has a 1/2" collet and draw-bar. We mounted the mandrel and got the same run-out. We took a wee bit of the shoulders of the nut just in case any were hitting the collet on the inside. Not much improvement. The last thing I tried was to reduce the tightening of the nut to the bare minimum (maybe 1/15th to 1/20th turn) and the run-out was reduced to a more acceptable level.

As far as I can determine, The center screw is a modified phillips head machine screw with the area under the head turned to a taper which is drawn into the mandrel tube when tightened by the nut. The taper on the machine screw is less than a precision process and the more you tighten the nut, the more it magnifies the inconsistent taper that spreads the mandrel apart and therefore causes more run-out. Less draw... less run-out.

I will try the four-jaw chuck tomorrow. As it stands, if the mandrel works with a minuscule amount of draw on the center screw, it will be within reason... far from perfect, but acceptable.

A tool and Die maker friend looked at it and has an idea or two for a modification that we might try.
 

Randy_

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I think a fair number of these mandrels have been sold and I don't recall any other reports of problems. That being the case, I think you are looking at a bad unit rather than a bad design. At this point, you might be better off contacting Bill for a replacement rather than spending time trying to fix the one you have.
 
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