The Beall Clock Forum

General => Wheels and pinions => Topic started by: Dave on December 10, 2010, 04:52:52 AM

Title: Harrisons gearing.
Post by: Dave on December 10, 2010, 04:52:52 AM
Hi All, i have the book Sleeping in oblivion which tries to describe how to make Harrisons final sea regulator, i say try as it is so darn hard to find some of the info you need. The wheel work is in brass but i would like to try and make a version of my own in seasoned Oak, my main question is what (cut) of wood is the strongest for shear strength, the main wheel is 8 inch diameter with end grain let into the rim of a solid Oak board but the teeth are only 2mm thick x 8mm wide, i have a picture in my mind of quarter sawn Oak end on which i think would be the strongest option but what do the experts think, cheers Dave
Title: Re: Harrisons gearing.
Post by: chuckknight on December 12, 2010, 07:07:38 PM
Is your intention strength or stability?

The forces involved within a clockwork are not particularly great.  But, the consequences of movement within the wood's grain are significant.

Multi-ply plywood is considered best for stability.  Beautiful plywood can be easily made with a resaw, or just glued up from common veneers.
Title: Re: Harrisons gearing.
Post by: Dave on December 17, 2010, 02:06:27 AM
Hi Chuck, i am after both strength and stability, i cut an 8 inch dia Oak blank and brought it into the house for a couple of weeks, (it cupped) which surprised me as this wood is well over 100 years old so i now know that each wheel will have to be built up of several wedge shaped pieces to make each wheel with the grain running from the centre out to the edge. Each wheel will have a rebate cut into the edge and end grain let in which will form the teeth, this is how Harrison made his wheels and i want to keep as near to his principles as possible, my main concern is which sort of wood (cut) to let into the edge, i am looking for strength here and i am trying to visualise which part of the Oak to use, whatever the outcome i will have to do experiments for shear strength as this amount of work on one wheel alone will be considerable. I have considered letting brass segments into the rim but this will be out of keeping with Harrisons ideas, cheers Dave
Title: Re: Harrisons gearing.
Post by: Joe Redburn on February 08, 2011, 02:43:05 PM
Dave
Any wood has it's greatest shear strength across the grain.  IE 90 degrees to the length of the grain.  You could cut the teeth on the edge of the wedge and skip the inserts.
When you cut wood, you must cut two opposite sides or the wood will twist, cup or curl.  It is better to cut 4 sides.
It would help if you cut half of the wedges from left to right and the other half right to left and alternate then in the wheel.
Regards
Joe
Title: Re: Harrisons gearing.
Post by: Dave on February 09, 2011, 11:46:36 AM
Hi Joe, thanks for the reply, i am finding more and more as i research about Harrisons wooden clocks, there is an x ray of one of his wheels which he built up the core from slow growing Oak and used fast growing Oak for the teeth which has me puzzled a bit as i always thought the slower growing wood would be the tougher of the two. I am working on an idea of using ply for the inner core and facing with Oak which should look like the original articles. I have gathered quite a bit of quarter sawn Oak from friends and have enough for this project, i still have to do the strength tests though which should be interesting to the group members, will be in touch, Dave