Author Topic: Pen Mandrel  (Read 9675 times)

Arkwright60

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Pen Mandrel
« on: December 08, 2012, 09:20:11 AM »
Can anyone tell me what I am doing wrong.

I have attempted to mount two pens on a pen mandrel, on both occasions the wood/barrel spins and does not hold.

I believe that I have glued the tube correctly, trimmed the ends of the blanks, put the correct spacers on and tightened up the mandrel.

Offline Philip Green

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Re: Pen Mandrel
« Reply #1 on: December 08, 2012, 10:50:02 AM »
Most mandrels hold two half pens.

Can you post a photo showing the end of your prepared pen blank prior to mounting and another of the pens mounted on the mandrel?
Philip from sunny St Issey

Arkwright60

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Re: Pen Mandrel
« Reply #2 on: December 08, 2012, 12:05:58 PM »
Please find photo of pen blanks, trimmed and Pen mandrel assembled.

Offline Philip Green

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Re: Pen Mandrel
« Reply #3 on: December 08, 2012, 01:21:40 PM »
I can't see anything obvious. It looks like you trimmed the blank until the trimming tool shines up the end of the brass tube which is what I do.

I recently saw a turner on You Tube using pliers to tighten the knurled wheel but I just use my fingers and I have rarely had a problem. If the blank does slip, I simply tighten a little more.

One thought that has occurred to me is that my mandrel is adjustable so that I can shorten or lengthen it for turning different size items. If this is not adjusted correctly, the knurled nut simply runs out of thread so the blank would not be secured correctly. I expect yours is also adjustable.

Philip from sunny St Issey

Arkwright60

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Re: Pen Mandrel
« Reply #4 on: December 08, 2012, 01:48:53 PM »
I have tightened as much as I can by hand, also ensured there is enough thread on the end.

Perhaps I will try tightening using pliers.

Thanks for looking any way.

Offline George Watkins

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Re: Pen Mandrel
« Reply #5 on: December 08, 2012, 03:37:44 PM »
what type of mandrel are you using?
some have an allen key to hold the stem into the morse taper carrier some rely on the carrier being tight in the headstock to squeze the stem.

which bit is slipping?
is it the blank on the mandrel stem?
is it the mandrel stem in the morse taper carrier?
is it the morse taper in the lathe?


Offline Martin Lawrence

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Re: Pen Mandrel
« Reply #6 on: December 08, 2012, 04:17:36 PM »
 Stands a chance of the wood turning on the tube.  I always rough up my tubes, seal the drill hole before glueing allow to dry before applying glue and I use an expanding polyurethane, super glue goes brittle and in time can loosen on the tube.

Hope this helps.

Cheers Martin
Martin Lawrence

Arkwright60

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Re: Pen Mandrel
« Reply #7 on: December 08, 2012, 07:16:33 PM »
Hi, George,

It is a Rotur mandrel.

It is then pen blank that moves around the mandrel shaft.

In order to get the knulled nut on the thread I have used two sets of bushings, parallel sides and tapered. I have noticed that the mandrel shaft is held on by an allen grub screw, so I am going to see if I can shorten the length and use only one set of bushings.

Stephen

ru55ell1

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Re: Pen Mandrel
« Reply #8 on: December 08, 2012, 07:26:37 PM »
Cant see your location on your profile, where are you based ?

thebowlerhattedturner

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Re: Pen Mandrel
« Reply #9 on: December 08, 2012, 09:29:58 PM »
Something you may be doing, and please do not be offended but I do not know how experienced you are, when the pen blank is first mounted and you are trying to take the corners off there is more leverage when you are cutting than there is when the blank is rounded, before you do something that may damage your mandrel just try sharpening your chisel and taking a very fine cut, it may benefit you if you turned the speed up a little bit. I know this sounds very basic but this is a common occurrence with those new to pen turning. Taking a slicing cut reduces the amount of leverage the cutting action produces.
Hope this helps
Regards
John BHT

Offline Roger Groom

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Re: Pen Mandrel
« Reply #10 on: December 08, 2012, 09:43:43 PM »
I'm most probably going to show up my ignorance of the subject now, but I have never seen bushing kits which were tapered where they butt up to the brass tube. I 've always believed that the bushes were there to give you the correct diameter to match the pen kit fittings. There is very little contact between the taper and the brass sleeve. Could this be the problem. Someone put me out of my misery!!!
Roger G

Offline john taylor

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Re: Pen Mandrel
« Reply #11 on: December 09, 2012, 04:39:03 PM »
Tapered bushes have been around for some time now, about as long as the full kits have been sold, this way they can say everything you need to turn pens.   They do have there uses but I prefer using the correct sized ones for each kit.

Does this only happen when you are roughing it down to round or all the time?

Looking at your picture there is a knurled nut and an ordinary nut is this correct?

john

Offline Paul Hannaby

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Re: Pen Mandrel
« Reply #12 on: December 10, 2012, 11:39:13 PM »
I think your problem is because you are using the tapered bushes. Use only the square ended bushes and you will get much more friction between the bushes and the pen blanks. Adjust the length of the mandrel to suit this configuration. The knurled screw shouldn't need to be more than hand tight when used this way.

Over tightening the tapered bushes will distort the end of the brass tubes and then you will run in to difficulties when assembling the pen so they are best avoided for the standard 7mm tubes.

Arkwright60

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Re: Pen Mandrel
« Reply #13 on: December 14, 2012, 05:17:04 PM »
Many thanks for all of the comments and assistance.

I have now managed to complete my first three pens.

The solution was a number of issues.

Luckily the mandrel was adjustable, so I adjusted it so that I just did half a pen at a time, also I did not use the tappered spacers.

Certainly adjusting the mandrel so that only one set of spacers are used seems to be the key, either with only half the pen or with both halves.

Again many thanks.

Stephen :)

ru55ell1

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Re: Pen Mandrel
« Reply #14 on: December 15, 2012, 12:08:47 AM »
You really should be able to have both halves of your pen on the mandrel at the same time :-)