AWGB Woodturning Forum
General Category => Tool tips & reviews => Topic started by: Arkwright60 on December 08, 2012, 09:20:11 AM
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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.
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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?
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Please find photo of pen blanks, trimmed and Pen mandrel assembled.
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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.
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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.
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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?
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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
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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
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Cant see your location on your profile, where are you based ?
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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
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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
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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
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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.
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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 :)
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You really should be able to have both halves of your pen on the mandrel at the same time :-)
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Hi, Rus55ell1,
Yes I do know, I started with one half then once I knew it worked it put both halves, the key was to adjust the mandrel so that I did not need to use both sets of bushes, once I realised that it was adjustable then everything was fine.
So once again thanks to everyone that pointed me in the right direction.
Regards,
Stephen A
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I remember some of the issues i had when turning my first few pens and it was a case of systematically solving the problems as i encountered them so i've written a brief check list which may be of help.
I usually use a set of square bushes of the correct size for the pen tubes i am using as mentioned by another writer here. These then provide the necessary grip between the pen blank and the mandrel ready for turning. A high speed is a must and so too is a fine cut on each pass to achieve the best results.
In relation to the pen tubes it is important to rough them up with abrasive prior to gluing, do not glue the tube home untouched by abrasive as the tube is far too shiny to affect good adhesion, this will prevent slipping once on the mandrel.
When gluing the tubes in, ensure that the glue covers all parts of the brass tube (especially with acrylic) otherwise chip outs may occur. Allow the glue enough time to cure and then use the appropriate barrel trimmer to reduce the pen blank pieces to exactly the size of the brass tubes (You should be able to see the shiny brass end just level with the pen blank on completion of this process).
Place the blanks onto the mandrel separated by the appropriate bushings and tighten up the knurled knob by hand. Do not over tighten as you may distort the mandrel itself or damage those nice square pen barrels you've just done. You may need to periodically check the tightness of the knurled knob now and again (Especially if you hear a noise).Ensure that the tail stock is bought up to the end of the mandrel and secured in place. Do not push/advance the tail stock up to far as bending of the mandrel may again take place, ideally just enough to support the end of the mandrel and no more. This should solve your problems.
kind regards
Brian Hensby