Large hole to ream out...

[Andy Coates]

Hello all,

I have a problem. No. Not that one.

I have to produce a tapered hole in lignum, two in fact.

One is 25mm to 28 mm over 60mm depth.

The other is 28mm to 31mm over 70mm depth.

I can't locate a supplier for a reamer with sufficient depth...so...any ideas?

I'm considering making a "saw blade" reamer from saw blade stock and a turned conical body, but thought I'd ask before I take the step of trying to make one.

Any advice gratefully accepted.

[thebowlerhattedturner]

Hi Andy,
          whenever I have to do stuff like this I go to the market tool shop and buy cheap spade bits and grind them to what I want. Sometimes you may need 2 or 3 different widths to get the depth (if you know what I mean) but it works for me. In the past I have ground a machine hacksaw blade to the required angle and gently pushed that in when the work was turning on the lathe. (I don't normally tell people this but it's only you and me!)
Regards
John BHT

[BarryMobbs]

Hello Andy,
 I would try to do it by step drilling a series of holes or using a square box scraper to achieve the same effect. Then mark the 28 diameter on the outside and use the sharpened side of a scraper to create a straight line between the 25 dia at the far end and the 28 diameter mark. I would make a plug with the same taper to fix abrasive to for final adjustments by sanding. 

[hughie]

I can't locate a supplier for a reamer with sufficient depth...so...any ideas?

Would have thought if you did it might prove to be very expensive, not exactly common sizes.
I suspect you will have to make your  and I think a simple blade reamer should do especially if you rough turn as much as your able. The saving grace is that it lignum and not some other less helpful timber.
Using spade bits is ok, except here the depth is a problem, you might need several covering various sections of the tapered hole, could be messy.
If your able to locate some 3mm 'ground stock' or 'gauge plate' from a local engineering supplies
https://maccmodels.co.uk/index.php?cPath=286
Cut a flat plate to the dimensions of your hole, mount it on a suitable rod to fit into your chuck on the tailstock. You will need to put some relief angle on the blade edges prior to hardening around 5-7' should do it. This gauge plate can be easily hardened with a good blow torch etc and quenched in water. Just heat it up to a 'cherry red' and dip into the water vertically so as to minimise any distortion. This will produce a very hard blade, ideally some tempering would be nice. But if your not so familiar with this process just leave hard.
Stone up the two edges till razor sharp, bearing in mind its carbon steel and heat will effect the hardness. Low revs and patience it should work out fine.

[BrianH]

Just a small addition to Hughie's words on hardening/tempering of high carbon steel. If you harden as described but quench in oil rather than water the steel cools a little slower and so the result is a little less hardening effect, which might mean you can ignor the tempering. I've done this with a home forged hook tool (the use of which I never did master.... but that's a different story!) and it worked for me.
Best
Brian

[Nige7]

Very new to woodturning but more experience with metal. On a metal turning lathe this would be easier but it strikes me that the headstock on my new lathe will rotate. How about working out the angle required, turning the headstock by the relevant angle then fitting a home made boring bar into a chuck mounted in the tailstock using the tailstock to feed the boring bar through a predrilled hole in the Lignum

Nigel