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simple mandrel

PostPosted: Mon Nov 17, 2008 9:07 am
by robin wood
Ranger Kris was asking about mandrels. Some folk may get put off bowlturning by the thought of having to buy expensive stuff like hooks and mandrels. The difficult bit is not the tools but the learning to do it, it is much more difficult than spindle turning but the tools are easier to sort out than you would imagine. Anyway the mandrel.

I use spiked mandrels and have for more than 15 years. The mandrel design you see me, Ben Orford, Gavin and others using is not so much traditional. I loosely based it on Lailey's but adapted it to suit blanks that are cut out with a very flat face cut with chainsaw or bandsaw. It is not what I would recommend for a beginner making their first bowl. This is what I suggest, it was commonly used technique historically too particularly in viking times.

Turn a spindle from hard wood around 2" diameter, if you have time, let it dry for a couple of weeks indoors then turn it back round but you can use it green, maybe make 2 use one green and put the other to dry. Turn the end 1/14" down to 1 1/4" diameter or fractionally over. Drill a 1 1/4" hole into the centre of your blank, perpendicular to the flat face (That's the difficult and important bit) Now whack the mandrel into the blank and mount the lot on the lathe. Turn your bowl and at the end after the core has snapped out, split the core to retrieve your mandrel. A mandrel like this takes only a couple of minutes to make and will make 40 or 50 bowls, plenty for most folk.

Re: simple mandrel

PostPosted: Mon Nov 17, 2008 10:00 am
by paul atkin
robs sugestion works very well, just remember to leave a largish size core around the mandrel other wise it can crack out before you have finished the bowl, as i found out :oops:

Re: simple mandrel

PostPosted: Mon Nov 17, 2008 10:05 am
by gavin
robin wood wrote: The mandrel design you see me, Ben Orford, Gavin and others using is not so much traditional. I loosely based it on Lailey's but adapted it to suit blanks that are cut out with a very flat face cut with chainsaw or bandsaw.

If you use mandrels fitted with tangs, you can decide
    1. to drive the tangs all the way in and so have the mandrel-end touching flat against the bowl-blank face
    2. to leave the mandrel-end clear of the bowl-blank face.


Option 1 will make your mandrel more secure against shock-loads UNLESS the tangs should work loose. In which case, you must try fitting a mandrel with a bigger set of tangs, with the consequent risk that your mandrel-core in the bowl will shatter.

If your mandrel should work loose, Option 2 allows you to remove your work, and tap the mandrel tangs in a little deeper.

I find I now prefer to split the bowl-blank with a froe, rather than bandsaw or chainsaw it. If the resulting froe-split face is irregular, I will flatten that with a few axe blows and then drive in a mandrel with the tangs part-visible. So the mandrel end is NOT touching the bowlblank-face - see option 2. To do this I use tangs with approx 20 degree taper.

A beginner is very likely to get digs causing a shock-load and so loosening the tangs. That shock-load is absorbed better if the mandrel-face touches the blank. I start a beginner on Option 1 i.e. with the tangs buried in the work and the mandrel-end touching the face.


robin wood wrote:Drill a 1 1/4" hole into the centre of your blank, perpendicular to the flat face (That's the difficult and important bit)

If you have a drill press, aligning a right-angle it should be easier. But don't be precious about attempting it with a brace and bit - just have a go! If it is too eccentric, take another blank and have a go with that. You could also drill the hole first in the half-log and then axe or saw the blank perpendicular to the hole.

You could also axe out the blank with the mandrel stub protruding - the "all-in-one" version. It would be more tedious ( you cannot re-use that mandrel!) , but it does work.

Re: simple mandrel

PostPosted: Wed Nov 19, 2008 7:48 am
by RangerKris
Thanks again for the information in the above post i am full on at work right now. but will get round to this soon.

Re: simple mandrel

PostPosted: Wed Nov 19, 2008 12:34 pm
by Follansbee
robin wood wrote: about mandrels. Turn a spindle from hard wood around 2" diameter, if you have time, let it dry for a couple of weeks indoors then turn it back round but you can use it green, maybe make 2 use one green and put the other to dry. Turn the end 1/14" down to 1 1/4" diameter or fractionally over. Drill a 1 1/4" hole into the centre of your blank, perpendicular to the flat face (That's the difficult and important bit) Now whack the mandrel into the blank and mount the lot on the lathe. Turn your bowl and at the end after the core has snapped out, split the core to retrieve your mandrel. A mandrel like this takes only a couple of minutes to make and will make 40 or 50 bowls, plenty for most folk.


Good suggestion. I made one of these years ago, and still use it, although I rarely make bowls. If I had to guess, I'd say I've made 60 bowls with it, but it's still working. the largest I make is about 8" or 9" in diameter. Mine's a good deal thinner than Robin suggests, but still works. My tenon is 5/8ths of an inch thick, about an inch long. At some point, it got too thin for my 5/8" bit, so now I stuff a shaving around the tenon when I mount it. works fine.

Re: simple mandrel

PostPosted: Fri Nov 21, 2008 11:47 pm
by Mark Allery
thanks guys,

that really helps demystify the mandrel for those of us thinking of crossing over to the dark side......... :-)

cheers

Mark

Re: simple mandrel

PostPosted: Wed Mar 04, 2009 7:10 pm
by Derek Masselink
I'm in the process of making a bowl mandrel. The comments associated with this thread have been very helpful.I was wondering how big the tangs should be? I have some 3/8" rod and am wondering how far they should be "buried" in the mandrel and how far should they protrude? Any help with the would be most appreciated.

Derek

Re: simple mandrel

PostPosted: Fri Mar 06, 2009 9:38 am
by paul atkin
hello derek my tangs stick out about 15mm or so and are buried in about 40mm, i tend to use threaded bar and drill the holes deeper, this gives the option of winding them in or out a bit as the need may be, hope this helps

Re: simple mandrel

PostPosted: Fri Mar 06, 2009 3:15 pm
by Declan Kenny
robin wood wrote: Turn a spindle from hard wood around 2" diameter, if you have time, let it dry for a couple of weeks indoors then turn it back round but you can use it green, maybe make 2 use one green and put the other to dry.


Perhaps we could use the uneven drying to our advantage? As the mandrel end will naturally season slightly oval-shaped, would it grip the blank even tighter if it was turned, banged in and left to its own devices for a couple of weeks? Much like the chair-makers who use the same technique for their tenons. Just a thought.

Re: simple mandrel

PostPosted: Fri Mar 06, 2009 4:09 pm
by Robin Fawcett
If you go down that route Declan you'll need a fresh, new, green mandrel for each bowl you make !

Re: simple mandrel

PostPosted: Fri Mar 06, 2009 4:11 pm
by Declan Kenny
...and that is exactly why I need to spend more time out in the workshop and less on the computer!
Cheers,
Declan