I saw a neat project in this book.....
I scanned the patterns from the book, imported them into sketchup, and scaled them correctly. I will use 1/4" diameter dowels to connect the links. I drew a link in Sketchup.
From a design point of view, you want the distance between link centers to be slightly larger than the OD of the links. If the OD of the links is 1/2", you want the centers to be more than 2 x 1/2" = 1"............and the pattern is 1-5/32, so this should work fine.
I also imported the drive gear design into Sketchup. It has 17 equally spaced 1/2 circles to drive the chain links.
I was surprised the 1/2 circles had a diameter of 1/2"...............not the 1/4" you would expect to match the dowels?? The distance between the drive half-circles is also not correct? As shown below, the center of the drive half-circles is 3/64" off from the center of the links.
You probably want the drive diameter to be slightly bigger than the 1/4" dowels on the links, but not 1/2" diameter........to allow for manufacturing tolerance stack-ups when making the links. I would think 5/16" would be fine, or maybe even up to 3/8" diameter.
If we stay with the link design, which appears to be ok...........then we need to adjust the OD of the drive gear to get the right distance between link centers.
I used Sketchup to determine what the 6" OD of the drive gear should be changed to, to fit the chain links......
So instead of the 6" OD specified in the book, it should be 6-9/32" to exactly match the link design.
The little decorative holes are a little too close to the chain links, I will move it inwards a little bit. The drawing above uses 5/16" diameter for the drive holes, just a smidgeon bigger than the 1/4" dowels. I will probably make a few parts and make sure it works ok before I scroll saw 52 chain links. My improve design is shown below.
It is not unusual for plans in books to have errors, I have found many over the years. In this case, if they were trying to round to the nearest 1/16", they should have picked an OD of 6-1/4, which is close to the actual dimension of 6-9/32"............but they chose 6.0 instead. Since I will print out the pattern from sketchup and glue it to the gear blank, I can scroll saw and drill exactly to the pattern.
The book does say to layout the gear blank first with a compass, then use the same distance between drive teeth and transfer that to the center distance on the links, which would fix the problem. The pattern for the gear shows the wrong distance though.
The material list says to use 5/16" thick wood for the links, but then the instructions say to plane it down to 3/16" thick?? Why didn't the material list say to use 3/16" thick wood?
The book also says to whittle the outside of each link to give a curved finish. I am not hand carving 52 links, that is like an accident waiting to happen with a sharp knive, plus very time consuming. I plan to stack several layers of wood, then "gang" scroll saw out the links.
A rounded edge would look nice. It is probably not important what the actual link thickness is, because you just adjust the 1/4" dowel length accordingly. I have an 1/8" round-over router bit, I need to see what the minimum thickness is for the bit to work. Holding the link while routing is a challenge. I could use 2-sided tape or hot melt glue, will have to see.
I checked my router bit, 1/4" is about the minimum thickness you can round-over, because you need some material for the ball bearing guide to run against. With 1/4" thick stock, you can only round-over 1 side, there is not enough material to do both sides because not enough material for the ball bearing guide.
Just rounding over 1 side should be ok. Before routing, I will try drum sanding on the drill press and see what that looks like.
Process I will use:
1. Drill 1st hole in links
2. Take fixture, extend bit down into link hole, clamp fixture to drill press table, and lock table
3. Drop link onto fixture over 1/4" locator dowel
4. Rotate link to line up with pencil tracing of link on fixture, hold by hand
5. Drill 2nd hole
The model will want to tip over when you crank it with a vertical layout, so I am going to switch to a horizontal layout.
I wanted to increase the distance between gears slightly, and therefore needed to know the distance between gears. I tried standard internet calculators and they either gave me an error or a wrong answer. I'm guessing they are set up for standard steel chain and won't handle other size chain?
So, I made guess one for the center distance and laid out the links in sketchup, and measured the error from the link to the gear. I moved the center distance close in sketchup and calculated the error again. I put the data into Excel and laid out a y=mx + b line to get the center distance with 0 error. I put this into Sketchup and got close enough. I will have to do trial and error anyway with the actual chain and gears to get the best fit. On spur gears, I have to add about 3/32" between the theoretical center distances to get good running gears.
I was killing some time, so searched youtube on wood chain. Found this video a guy made on how he made wood chain.
He made a jig for the router table where he rounds the edges on 2 links at a time...........I might have to try this on my project.
Also found a video about a program that generates pattern for various types of wood chains on this link.
I wrapped 2 layers of 1/4" thick red oak with blue masking tape, then white Elmer glued the paper pattern from Sketchup on top.
Then I drilled 1/4" diameter hole in each link. Then to the scroll saw.
I drilled a 1/4" hole in a piece of 3/4" thick scrap pine, then put a dowel in it. I pencil marked the outline of the link.
I locked down the drill press swivel table, then clamped the fixture to the table.
I put the link's 1st hole in the dowel, lined up the link with the pencil outline, then drilled it.
I can put this set-up back on the drill press by lining up the 2nd hole with the drill bit, then locking the swivel table and clamping down the fixture.
This method works ok, except it splinters the red oak when the bit breaks through. I have no fix for this since there is not stock in the fixture hole to prevent the break-out.
I borrowed the idea for the holding fixture from the Youtube video noted above. It did not work well, it kept rocking on the router table. I added 2 little boards, 1" high, to equal the 3/4" high fixture piece + 1/4" thickness of the link. This worked ok, but since the links do not exactly match the fixture links, I get some router bit burn. I then took the links to the drill press and drum sanded with 220 grit, and removed the burn marks. The links are done now in terms of process.
The process I used was:
1. Blue tape 2 blanks together, glue pattern on top.
2. Drill 1 hole in each link
3. Scroll saw each link, peel off blue tape
4. Drill 2nd hole in each link using fixture
5. Round over edges on router table
6. Sand with 220 grit on drill press
An alternate process could be:
1. Blue tape 2 blanks together, glue pattern on top.
2. Drill 1 hole in each link
3. Scroll saw each link slightly oversize, peel off blue tape
4. Drill 2nd hole in each link
5. Use edge beading router bit to make curved edge on link
6. Sand with 220 grit
This is the type of bit I am thinking of shown below. I already have 6493 bit from a previous project.
I thought the beading router bit shown above would give a much nicer and rounder edge on the links, so I tried it.
I scroll sawed 2 links just a hair oversize to leave some stock for the router bit to remove. Started bead bit on 1st link, and ka-ching........the bit hit a spot where the grain changed direction and it ripped a piece out of my link!! So much for that idea.
I was not happy with using the round-over bit because the bearing on the bit would often follow the fixture link, and not the piece to be worked. Then the light bulb came on.....When I drew up the links in sketchup, I checked my round-over bit........and decided if I used 1/4" thick links, there would be enough stock on the link to guide the bit.......including when I flipped the link over to the other side.
I took my Dremel and removed material around the fixture link so it was smaller than any of my oak links. Presto..........that set-up worked the best of any I have tried!! Less burn and a more consistent edge shape also.
On both drilling the links and the 2 gears, I ran a 1/8" diameter pilot bit through first, then ran Forstner bit half-way through, flipped over and finished.........this eliminated tear-out
I chose to use 1/4" diameter dowels for the links, so I chose a slightly bigger 5/16" hole size for the notches in the gear.
After trying the first few links on the 1st gear I made, they fit ok.......but it struck me the notch holes could be quite a bit bigger and it would still work fine......like 3/8". We will see how well my design works when we get both gears and all chain done........and see how well 1 gear drives the chain and other gear.
I was able to stack 4 pieces of 1/4" oak and saw them at the same time. I had Sketchup paper patterns for 8 links, so I got 8x4 = 32 links from that stack.
I have learned on my past projects with wood gears to always test the center line distance between gears, before making the final piece that holds them. On my wood gear projects, I usually have to add 3/32" to the theoretical center distance. I verify this first using a piece of cheap pine.
On this one, I just can't use a scrap piece of pine, because the chain will hit the pine piece. Maybe I will go ahead and make oak spacers that will go in the final model, and use them for testing?
My design has 15 links in each of the 4 rows, so it takes 15x4 = 60 links..........and I made 4 spares.
I did lose 1 link on the router table with the round-over bit, it blew a chuck out of.
I was out of hinges, so I used Plumber's Strap instead. This fixture lets me drill the toothpick holes in the center of the 1/4" axles at the right spacing. I'm using a 3/32" bit for the toothpick holes.......my toothpicks are round.
My theoretical gear center was 7.5 inches. Once I got the links assembled, I put them on the 2 gears, and my gear center distance is between 7 and 7.5 inches, so ok.
The photo below shows how I screwed the 3/4" thick 2" OD spacers to the vertical base. This allowed me to change the gear center distance by moving the screws and spacer on the RH side. Once I got a center distance I liked, I drilled the 3/4" hole through the vertical base because it has to rotate with the gear and crank.
I chose to start with 7-3/8" center versus the theoretical of 7-31/64" from Sketchup. I had no toothpicks in the axles during these tests.
The good news is the model ran :) But sometimes the top wheel would start to get out of the chain dowels, indicating the chain is not tight enough. I made a video of this test, and you can see some slop in the chain as it runs.
I guess as you stop and think about it, the gear centers may need to be bigger than theoretical, because of all the tolerances involved with the axle holes.
I also think the gears may need to have a lead in chamfer or radius on the OD, to help keep the center 2 rows of links spread out so they fit on the outside of the gear?
Hopefully, the 2 gear axles are staying pretty straight on not bending too much. I plan on gluing the 3/4" thick 2" OD spacers to the vertical base board, to stiffen the axles for the gears at final assembly.
I'm hoping to get by with a fixed gear center distance, and not have to make and adjustable method of setting the distance.
I checked the bottom gear shaft, it was solid...........but the top gear shaft was leaning down significantly. I held the dowel up from the back, which is probably closer to horizontal like it should be...............and chain ran smoothly. With dowel in right position, you can push on chain between gears, and most of the slop is out. I think my 7-3/8" gear center distance might be ok.
I was catching some on links entering the gears. I checked the book, and it said to shape the edge in a V-shape, it is a poor illustration. I went to my round-over bits and selected an 1/8" roundover bit...............I wanted to use the 1/4" bit, but I was afraid I would not leave enough stock in the center for the bearing to ride on when I went to do the 2nd side. I tested the set-up again after rounding over the edges of both gears, and the binding seemed to stop. I have a 45 degree chamfer bit with a guide bearing, if the final model still catches, I could route the edges again with this bit.
2 gears..............went with Cherry colored stain.........which gives red oak a reddish hue. I will put 1 or 2 coats of polyurethane on next.......and I think it will work with the mineral oil I am going to put on the chain.
going to leave the 1/4" dowel pins and toothpicks with no finish except mineral oil.
On the links, Golden Oak stain, no poly, then mineral oil.
vertical base and horizontal base, don't know yet, probably stain and poly.
I ended with re-drilling the axle holes with the 17/64 bit I have, to lower the friction on the 1/4" axles.
Everything is red oak except the crank, which I plan to use maple.
For the 2 gears, I went with oil based cherry stain........and 1 coat of gloss polyurethane.
For the links, I went with Golden Oak and 1 coat of poly, I tried not to get any poly in the axle holes by using an artists brush.
On the vertical and horizontal bases, I will go with no stain and 1 coat of poly.
For the 1/4" birch dowels, I went with a yellow water based dye. My powder bottle is now 11 years old, and the powder is still fine :)
I made a 3/4" thick spacer with 2" OD for each gear. To make the gear center adjustable during try-out, I used 2 wood screws in each spacer......to screw the spacer to the rear vertical base.
I started with 1-3/8" as my preliminary testing indicated. This was too big.........I got the chain hanging down on the bottom.......and the axles slipped out of their semi-circles.
I then went to 1-9/16", and this is really tight. I used a square straight edge and found my vertical base piece is bending. I added a piece of pine across the back to stiffen it up........but the gear is very hard to turn......and I am still slipping on the axles to their semi-circular holes.
I can try something between 1-3/8" and 1-9/16" gear centers..........like just under 1-1/2". But I suspect I will still get slippage of the axles out of their semi-circles?
I went back and checked the original plans. The plans called for 1/4" dowels for the axles, which is what I did. But on the gear, the plan had 1/2" diameter holes !!!!!! When I did my Sketchup design, I thought that was too much and reduced it down to 5/16"..............so I am 3/16" less in diameter than the plans. Maybe the bigger 1/2" hole is needed to keep the axles from slipping out of the semicircles.
I think I can drill my 5/16" holes to 1/2" on the drill press. I may have to make a fixture with the gear on a 3/4" axle and rotate it to each hole to redrill.
I tried a half-way point on gear distance, but still got slippage of the axles out of their semi-circles...........so I bit the bullet and redrilled both gears with 1/2" dia bit instead of the original 5/16" bit.........using a special fixture I built as described above.
I put the gears back on the chain and turned the RH one with a 3/8" dowel, and it seems to run ok.
I will restain the new drills holes with the cherry stain and then continue assembly.
Most of my axles are 2-3/8" long. I made the spacer inside the crank a standard 3/4" thickness, but some of the axles hit the crank!!
My Sketchup drawing only had 2" length, so I increased it to 2-3/8" on the axle by the crank, and it interferes :( Tomorrow I will have to rework the crank and add a 1/4" spacer to fix it. I think it will run smooth after that......and I can do final assembly.
I applied Johnson Wax to the OD and OD edges on both gears, because that is what pulls out the links when they enter the gear. It ran much smoother after I did this :)
The easiest way to rework it was to hand scroll saw off the handle, make a new 1/4" spacer, glue spacer onto existing 3/4" thick spacer, then glue crank back on.
I held the vertical base upright, and in the right position per my carbon tracing it on the horizontal base.......then marking both legs with pencil. I scroll sawed out the 2 holes, then put 1 screw in horizontally from the back. I have used this on several projects, and it works pretty well.
Every project has a few key things which must be right. In this project, I think the key is using 1/2" diameter semi-circles to drive the 1/4" dowels. If you use a smaller diameter semicircle, like 5/16", the chain tends to jump out of the semi-circles.
Another key item is the chamfer or radius on the edge of the drive gears. There is nothing to keep the inner 2 chain links in the open position except being driven out by the edge of the drive gears. With no chamfer or radius on the gears, my model bound up all the time. Once I put an 1/8" radius on both edges of each gear, it ran a lot more smoothly. I would have put on a 1/4" radius, but I was afraid there would not be enoough material left in the center of the gear teeth to let the bearing ride on when you routed the 2nd side.
I think something a little larger than my 1/8" radius would be even better and make an even smoother running model. I am not sure how I would do this, maybe buy a special 3/16" diameter round over bit? Chuck the wheels in the lathe and turn them more? Since my model works ok, I am not going to try to increase the radius on my model.
It is very time consuming to make the 60 links required. I don't know any way to speed this up.
This should be a fun model for the grand-kids and adults to play with!