Cutting HTD pulley(s)

[Jonathan]

I had a go at cutting a 30T HTD pulley on the router yesterday. I used a 3.1mm drill to make holes to match the profile of the teeth, then milled the profile using a 1/8" carbide cutter. Since the maximum tool diameter which can cut this profile is 3mm, the 1/8" cutter only reaches near the corners, but it still left a good profile which fitted the belt admirably first time:

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The holes were a bit rough, even with the flood coolant, so I may try a carbide drill or maybe mill the entire profile. The issue with milling the entire profile is the required cutter is very long and thin, so it would be slow unless I use the 4th axis as I have previously for XL pulleys.

Here's a video:


http://www.youtube.com/watch?v=hXxCQOqG8D4&feature=youtube_gdata

It would be entertaining to try cutting a non-circular pulley, so the driven pulley rotation would be some arbitrary function of the other pulley position, not just a simple ratio. Might be useful for something...

[Ricardoco]

Hmmmm looks interesting....Did you find all the dimentions somewhere Jonathan, or did you use some math trick and work it all out yourself?

Rick

[Jonathan]

Cambam has a plugin that draws 5M HTD pulleys, so I used that. However I did check it looked reasonable first by looking up the equations, which are very simple. You just find the pitch diameter (30*5/pi) and subtract a constant to find the PCD of the holes, then subtract a different constant from the PCD to find the external diameter of the pulley. Draw all those and round off the corners for each tooth, like this:

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It was a similar procedure for the program I wrote to mill XL pulleys (http://www.mycncuk.com/forums/g-code-corner/3051-some-gcode-generating-programs.html#post20134), but those were a bit more interesting since the tooth profile has to be milled, not drilled.