Thread Milling

[toddmaci]

All,
Does anyone know where to get a bit to do this? How about tool pathing something like this?

http://video.google.com/videoplay?docid=-8909242655409608351

Thanks,

Todd

[myxpykalix]

I think you could probably accomplish what you wanted with a "side reeding bit" like this:
http://magnate.net/index.cfm?event=showProductGroup&theID=202

I have one but have never used it for making inside threads.
This might be an oversimplification but take one of the spiral wizards and create a spiral based on your bit diameter and work diameter then change your X movement for Z movement.
You could do the same for your "nut" as you do for your "screw".

[toddmaci]

Jack,
I contacted the guy who submitted the video. He had the cutter custom made. I don't think the reeding tool would work as the beal tool threads are very broad.6 tpi

Todd

[donchandler]

You can buy a carbide tool, made for threading, that is similar in appearance to the one in the video. They have several sizes, depending on the TPI that you want to cut. MSC has them, they are made by Micro 100. About $80 as I remember. I have 1 that we use to do 8 TPI all the time. We also cut tapered pipe threads on plastic pipe. The tapered thread programing is a little tricky, but you can do it. We thread the hole and the male part with the same tool. Works great.

[Gary Campbell]

Todd..
the ShopBot CP command will cut those threads. You will have to select the spiral down parameter, in the case above of 8 TPI you can select .125 as the depth per pass. I would imagine there would be some trial and error to get the diameter correct.
Gary

[beacon14]

That's bizarre - I had bits exactly like that made earlier this year for that exact purpose. And I thought it was an original idea. I know why he makes so many passes for each nut - my bits both broke after 11 or 12 threads. I ordered a couple of 1/2" shank models but had to put the project aside and haven't had time to pull it back out yet.

The CP command with spiral plunge is the way to do it.

7430

[stevem]

Thread milling is very common in metal machining. Thread mills are available as off-the-shelf tools, although I don't think metal thread profiles are suitable for wood.

[myxpykalix]

David..thats neat, what broke the bits? You would think there would be very little strain on them.
I could see how you could make threads on your screw on an indexer with the right spacing toolpath but you couldn't with the nut.

7431

[harold_weber]

David, is that a sharp-edged inside corner on the shank of the tool where the diameter changes? That is the WORST possible stress riser you can have on the shank, so it should not be a surprise that the tool failed there. Take a look at "boring bar" at machine supply houses, they won't look like that.

[toddmaci]

Thanks for all the responses.
David, Did you cut the threads on the dowel rod on an indexer or did you stand it vertical and cut with the bit?

[beacon14]

I drew the business end of the bit but left the other end to the company that made them for me. I noticed the square inside corner when they arrived but it was too late by then. I wasn't surprised that they broke but was surprised how quickly they broke. Since the hole was pre-cut with a straight bit it didn't seem like there would be that much stress. Wrong I guess.

The replacement bits are much beefier and I made sure they machined a filleted corner where the shank steps down. Since it's a project for my own home there's no telling when I'll get back to it.

Since I don't have an indexer I did both the male and female threads with the custom bit and a spiral plunge CP command.

[mgranato]

Steve M, I've got some 3/4" PVC sheet discs (5") that I need to put male threads on and then make the mating female parts. Could you point me to where I could get the bits you are talking about?

[stevem]

http://www.harveytool.com/products/index.php?page_function=show_family&product_family =Thread+Milling+Cutters&category_id=1 (http://www.harveytool.com/products/index.php?page_function=show_family&product_family =Thread+Milling+Cutters&category_id=1)

http://www.sct-usa.com/tm10.asp

http://cmtechtools.com/solid-carbide-thread-mills.html?OVRAW=thread%20milling&OVKEY=thread%20m illing&OVMTC=standard&OVADID=584509513&OVKWID=6596 782513

DISCLAIMER: I HAVEN'T PURCHASED FROM ANY OF THE ABOVE COMPANIES OR USED THEIR PRODUCTS.

[stevem]

Short introduction to thread milling: http://www.sct-usa.com/millhelp.asp