Ferrules on the mandrel

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Ferrules on the mandrel

Postby Robin Fawcett » Sat Apr 05, 2008 6:33 am

I notice that Rob & Gavin both have metal (steel?) ferrules at either end of their mandrels. What are these for exactly ?

If I had them I would have wrecked the edge of the tools nearly every time I turn a bowl. The problem is I find it extremely frustrating and difficult to undercut the core using a hook tool - it usually catches and spirals back up into the mandrel no matter what angle of presentation I try. I have to resort to a spindle gouge for this bit.

What am I doing wrong ?
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Postby robin wood » Sat Apr 05, 2008 8:24 am

simple answer is presenting the hook at the wrong angle in just the same way as when a skew spirals across the work. I could show you how to do it but probably not describe it. Not sure if it is shown on any of my youtube turning vids but it may be worth looking closely at those.
Its not easy to describe because the angle you go in at depends on the shape of your hook tool. I can do that cut with any number of tools but they would all be held slightly differently. I think I tend to go in at about 8-9 o clock on the blank and then as `i get deeper drop to 7-8 O clock ie below centre height. The far edge of the tool is cutting and the cutting edge as it touches the wood is not far off vertical, it can be either open bit of hook up or open bit of hook down.
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Postby Robin Fawcett » Sat Apr 05, 2008 10:43 am

OK - but you didn't mention anything about the mandrel ferrules.
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Postby robin wood » Sat Apr 05, 2008 11:54 am

sorry yes I started putting ferrules on first on the end that you hit with a hammer because it stops the end splaying out and prolongs life. I put one on the other end too on all my small mandrels again to stop that end splitting as the spikes are driven into the blank. I reckon a mandrel without ferrules will certainly make more than 20 bowls maybe 50, I want a mandrel to do at least several hundred if not thousands. I started because Lailey had them on his and I had worn out a lot of mandrels.

When I first looked at doing this I thought I would have to get someone to weld up a hoop for me but the easy way is to pick up some old scaffold poles and similar of different diameters and cut a ring off the end with an angle grinder. At first I tried the old wheelrights trick of fitting the ring hot but it does not work on this small diameter, just turn the mandrel so it is slightly tapered and bang the ferrule on.
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How I make and fit ferrules on bowl-lathe mandrels

Postby gavin » Sat Apr 05, 2008 7:59 pm

I go to an engineering shop and have them cut me say 20 or 40 rings of pipe retrieved from their scrap bin: anywhere from 40 to 50 mm internal diameter will do. They will have a chop-saw or some other device to give you standard length, and wonderfully square-cut ferrules. I have them make mine 30 mm long, but guess you could have them 20 or 40 mm and it would not matter. I tried earlier cutting them myself with a hacksaw or angle grinder, but I could never get a perfectly right-angled cut. And if you don't get the ferrules cut dead square, the ferrule will twist and get stuck as you drive it onto the mandrel.

I would suggest you get that quantity of say 40 ferrules cut, as it is no bother to the man with the chop saw to do a run of them in 5 minutes, and it will encourage you to make many different mandrel shapes and lengths. If you did have an abundance of mandrels, you could even decide to leave mandrels in the work for subsequent re-mounting on the lathe to turn the work back to round again once it has shrunk and warped somewhat. ( I have yet to try this myself, so I am not advocating it firmly.)

I then hammer right round one INSIDE edge of the mandrel with a ball-pein hammer. That removes any burr and slightly flares the leading edge, allowing it to travel more easily down the mandrel.

I thank the wheelwright who demonstrated at Formby Bodgers Ball in 2005 for that ball-pein flaring idea. When he makes ferrules to go on wooden sledgehammers ( called variously a 'maul' or 'beetle') he also told me that sprinkling chalk dust on the ferrule helped the ferrule bind onto the wood once he had ball-peined the leading edge. And I have not found chalk necessary so far for the mandrels I have made.

With the bone-dry sycamore that I use for mandrels, I turn them to 1 mm more than my internal pipe diameter and whack them on. With the flared leading edge, it works fine. Do make sure the pith is in the center of the mandrel, so that the centre will wear evenly and stay central.

I use sycamore only because Philip Dixon suggests that Lailey used sycamore. I do reckon Lailey's mandrels look like sycamore, but I am no botanist. Perhaps Robin Wood can comment on Lailey's preferred species for mandrels?
Last edited by gavin on Sat Apr 05, 2008 8:16 pm, edited 1 time in total.
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Mandrel-core undercutting

Postby gavin » Sat Apr 05, 2008 8:11 pm

That under-cutting of the core is the single hardest thing to do, and I struggle to explain how I do it!
All I can suggest is that you experiment with your various hooks.
Ask yourself questions such as:

is the work PERFECTLY round? ( if it is eccentric, you'll really struggle )
Even if your are holding the shank perfectly still on the tool-rest, is the tool-tip flexing a bit, thus leading to an eccentric cut?
Would altering the tool-rest height help?
Would altering the tool-rest angle help? ( I suggest you want the rest to be lower on left-hand end so the hook-shank tends to be forced against the work rather than away from it.
How enclosed are your hooks? I think you are better with ones that have only a slight kink in them i.e. more of an 'L' than a 'U' - but I have not done enough comparisons to be dogmatic on this point.

Do stick with your hooks! If Robin Wood and Geo Lailey have found them most efficient, I think it follows you waste your time with anything else.
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