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Sunday, July 24, 2011

Homemade Wood Clock Construction

Last week I wrote about a homemade wood clock that I was designing in Solidworks. If you are curious there is a link to that post HERE, there are details about how it is going to work. If you don't want to read that post, the homemade wood clock design is as follows: I decided to make a clock that has an hour hand that stays upright, pointing straight up all the time and the face of the clock moves to tell the hour. Because the face is moving to meet the hour hand (instead of the other way around) the minute hand has to turn at a different ratio than in a 'normal' clock. To get that to work I designed a wood gear clock movement (gearbox) that has a 11:1 ratio with the face of the clock turning counterclockwise and the minute hand turning clockwise. Although I didn't make as much progress on this wood clock project as I wanted, I did manage to get some work done. I got all the gears done, the 'spindle bearing' figured out and the support structure made. Be sure to have a look at that last post I linked to above to see what I am trying to do.
Wood, Gears, Glue and Tools for the Clock
There are a few things that I got worked out in the design since last week and a couple of problems solved. One issue: I have never cut gears from wood before so this was a bit of a learning experience for me. To make the gear patterns I used an online Gear Template Generator from a site that I link to in the "Sites I Like" bar in the sidebar of my blog. Cutting the gear teeth started with printing out the gear pattern from the online generator above and gluing the template to Baltic Burch plywood. The Baltic Birch has a tight grain and the layers in the plywood are very thin making is good stable wood to work with. After getting the pattern on the wood I rough cut the gear out with a band saw then finished the teeth with a scroll saw and sanding. Getting the hole right in the middle of the gear was a challenge but I managed to do it. If anyone has any advice about making gears from wood I would like to hear it!

Rough Cutting a Gear on the Band Saw
I managed to get all the gears cut out and sanded down with few boo-boos and they seem to run smooth when I hold them together with a couple of nails in a board. Not too bad considering it's my first try with homemade gears.
Another design issue that I had glossed over in the SolidWorks CAD model from the previous post was the spindle bearing. I'm not sure what the correct clockmaker terminology is but I'm referring to the center spinning concentric hollow shafts that the clock hands are attached to. Have a look at THIS picture, the green cylinder in the center of the clock is that I am referring to.  In my case one of them is attached to the face of the clock but it's the same idea. I decided to go with brass tubing and a solid brass rod for this part. The solid brass rod 0.187 OD, is the innermost 'shaft' that will be connected to the minute hand. That shaft is a slip for for a brass tube that is 0.220 OD, that the face of the clock is attached to. The 0.220 OD tube is a slip fit for a 0.250 OD tube that is attached to the base of the clock - so it's stationary.
Clock Face (backside) and the Clock Base
The picture above shows the face of the clock, the back of it actually, and one piece of the clock base. In the center of the clock face you can see the 0.220 OD brass tube that is coming out of a smaller circular piece of wood. The smaller piece of wood is there to essentially make the face of the clock thicker providing more surface area for the brass tube to adhere to. I used Loctite Super Glue Gel to glue the wood together and to glue the brass tube to the wood. I roughed up the OD of the brass tube with a file and cleaned it with acetone to get a good surface to adhere to.
Also in the above picture you can see part of the base of the clock. There is a small piece of wood glued to it with the 0.250 OD brass tube just inside. Again the tube is roughed up, cleaned and glued so that the tube doesn't move. The tube 0.220 OD tube sticking out of the clock face is a nice slip fit into this 0.250 OD tube in the clock base and together then make a bearing so the clock face can spin relative to each other. What isn't shown here is the 0.187 solid shaft that fits inside the tube in the clock face and the gear that will attached to the clock face tube after it has been placed in the base. If you have any questions please email me at or leave a comment (or both!).
I decided that the next step in building this was to figure out where the number for the clock were going to be. I suppose that usually this could be the last thing that someone would do when making a clock but in my case I wanted to get it out of the way early. Because the face of the clock is turning and I wanted all the numbers to always be right side up, the numbers have to individually turn. HERE is a video that shows how this clock is going to look when it is running and you will notice that as the face of the clock turns all the numbers remain upright. To do this each number will be mounted to it's own small round disc and the discs will be mounted to the face of the clock with small bearings (or bushings). There will be a small weight on each number so it's heavier on one side (the bottom) and the heavy side will always point down naturally.
I wanted to get all the holes drilled in the face of the clock for the bushings while the clock was disassembled and easy to work with. Additionally I wanted to make sure that whatever I decide to put through the holes, bushings, bearings etc... were not going to interfere with anything behind the face of the clock.
Laying Out the Face of the Clock
I cut a small piece of scrap wood the diameter of where I wanted the holes for the numbers to be and drilled a 0.225 hole in the center of it so it would fit over the center tube in the clock face. Have a look at the above picture to see what I mean. I marked the face of the clock on each end of the scrap wood for two numbers across from each other and used a square to find a third point at a right angle. Now I could rotate the scrap wood until it was lined up with the mark made by the square and make a third mark opposite that one. Confusing? Email me! Essentially after doing this I had four marks on the face of the clock all directly across from one another and all forming a 'right angle' to the center of the clock. This of the 12, 6, 3 and 9 on a clock face.
Once I had those easy marks made on the face I had to add the remaining location marks for the numbers. To do this I used a divider and the scrap wood piece with a little trial and error.
Finding the Remaining Clock Number Locations
I divided out the space between two of the four marks on the face with dividers rotating the scrap wood tool to place the divider points. Once I had the new locations marked I used the tool to make marks directly opposite... confusing? If the first four numbers I found above with the square were the 12, 6, 3 and 9 then with the dividers I found the 1 and 2, using the scrap wood tool I could mark directly opposite the 1 and 2 to find the 7 and 8 locations. With the dividers set at the right distance it was easy to then get the 10 and 11 locations and with the tool mark directly opposite those - the 4 and 5.
That's about as far as I got this week. I did manage some pre-assembly of various gears and other components but there is still a lot of work left to do. More in the coming week(s) on this project and so far I can say this is a fun and interesting thing to build. I'll wait until this one is done before deciding if I'm going to make more clocks... ;-)

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