Cutting HTD pulley(s)

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:

Attachment 7579Attachment 7580

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=hXxCQ...=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...

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

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:

Attachment 7587

It was a similar procedure for the program I wrote to mill XL pulleys, but those were a bit more interesting since the tooth profile has to be milled, not drilled.