Having taken a few days to recover from the last workshop sessions; and since I get up early in the mornings, I decided to go into the workshop before my brother Steve came over to take me sea fishing in our boat.
The reason for my early start was the gear cutting request from Thomas, which at first sight was a simple task, but it turned into something both more complicated and a good learning experience. The main lessons for me were the lack of availability of reasonably priced cutters for the size required, and having to refresh my knowledge on gear cutting in general.
I did the sums in both imperial (DP) and for metric (MOD) since Thomas required metric finish sizes to enable me to find a cutter. I thought I had solved the problem when I found the right hobb for a very reasonable price. In the past I have used Tracy Tools based in Torquay (only a few miles from me) but they didn't have the sizes required. So Arc Eurotrade are certainly worth a visit for metric hobbs at very reasonable prices.
The Hobb purchased from Arc Eurotrade
However the hobb has a thread form so the blank to cut the gear on must be free to revolve, something the design would not allow for this project so it was back to square one. I decided therefore that it may well be easier to go back to the original plan and make a form tool of the tooth myself. This was soon made and I decided to make a new tool holder for the milling machine since I found the one I was going to use had a 20 thou 'wobble' which obviously would not do.
New tool holder for gear cutting
The last workshop session saw me make the tool and holder but because I was unwell, I could not for the life of me do the basic calculations (my excuse)to use my Vertex dividing head. Unfortunately the tables that came with the Vertex have decided to hide themselves, so I have to work them out each time unless they are in the data tables books I have. So of course the 15 divisions Thomas want's doesn't appear anywher since the lowest given is for 20.
Now it is relatively simple and John Stevenson has written quite a bit on gear and gear cutting (search Google) and there is an excellent book available written by Ivan Law (Workshop Practice 17 Amazon link on my main website) and anyone new to cutting gears should consider buying a copy. So once I had sorted out the numbers for the Vertex I wanted to check that they were right, hence my early morning start. I have decided that I will put gear cutting for novice engineers as part of my main website, hopefully adding a novices perspective.
After finding a scrap piece of brass of the same approximate diameter I secured it in the chuck and started to cut using the specially ground tool. I didn't want to take too deep just enough to count the teeth. So after 15 cuts I checked the piece and was more than just pleased to see the correct results. Whilst the tooth shape is not correct because of the depth of cut, trying the unfinished scrap piece on the gears Thomas supplied and it all looks fine so as soon as I am well enough to go back to the workshop it shouldn't take to long to finish the job.
The scrap piece of brass used as a trial for checking it is 15 divisions
I am working for Steelmans gears which is a leading gear cutters manufacturer and exporter of Gear Hobs, Involute Gear Hobs, Hub Type Shaper Cutters, Shank Type Shaper Cutters, Shaving Cutters, Chamfer Hobs, Sprocket Hobs and Straight Spline Hobs in India.
Nice post on gear cutting..thanks for this information..
I normally do not post these type of comments but this may be of interest to others. I have no personal knowledge of the company so this is not a recommendation.