On 1/3/2016 10:37 AM, Kirk Wallace wrote: > I have been looking at clock gearing off and on for a while. So far, I > have found that clock tooth forms are cycloidal, but not really. It > seems there is a British standard which is based on the ideal cycloidal > form but uses a circular arc for the curved part of a tooth, rather than > a cycloid, and clearance is added according to practical experience. I > haven't been able to find the contents of the standard, but I'm still > looking. My plan was to use a very small diameter (.015") end mill as a > universal gear cutting tool for thin wheels from sheet brass. The wheel > can be drawn in CAD, converted to g-code then cut in XY without using a > rotary axis. I would appreciate any links or information that could get > me closer to actually cutting wheels and pinions. Although, pinions are > a different kettle of fish.
One way to do it is design the gear in a 2D CAD program then export it to DXF to import into a CAM program to convert to G-code. The free emachineshop software has a gear wizard but it only does Diametral Pitch. However it allows for arbitrary input in the DP slot so with a calculator like this http://www.technobotsonline.com/gear-size-calculator.html you get the equivalent number to enter. An issue with it is it creates tooth profiles as a lot of short, straight segments. HEEKS CAD/CAM has a gear generating wizard that only does metric gears so to cut a DP gear you have to convert the other way from emachineshop. HEEKS' gear wizard uses curves for the teeth and its output is adjustable after creation. Select the shape and change the numbers. HEEKS costs $10 for the full version, but the only difference is the paid version doesn't put a demo notice in the G-Code output. That can simply be deleted with any text editor. FreeCAD's gear wizard is also metric only. http://www.freecadweb.org/wiki/index.php?title=PartDesign_InvoluteGear IIRC I couldn't get an exported file from it that would import into HEEKS. Why I got into this was a need to repair a 14 DP gear on one end of a spool gear in the reverse drive on a 1943 LeBlond Regal 13" 'trainer' model metal lathe. Most of the gears in its headstock are only 5/16" thick. Welded up all the teeth on the chewed up gear, put a pointed rod into a collet in my PLM2000 mill to center the gear under the spindle, clamped it down and set the origin to center. Then I fed it the G-code from HEEKS to make a lot of shallow passes with the largest endmills I had that were still smaller than the smallest radius in the tooth gullets. I made different G-code for different mill diameters. Ended up going over much of the depth repeatedly, broke all the little mills I had, despite using cutting oil, but the job got done. Other than finding someone with a shaper and either an old 14 pitch tooth cutter or the skill to grind one, or a hobber with an extra small diameter 14 pitch hob, it was the only way to fix it. The other gear on the spool was too close to use normal involute cutters or hobs. LeBlond quoted me $1500 and at least three weeks before they could think about making a new gear. (Probably would have to locate a retired machinist to come in to do the job!) --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
