Film-Tech Forum ARCHIVE: Drilling and tapping platter tree

This is topic Drilling and tapping platter tree in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=009636

Posted by Dan Chilton (Member # 2288) on 11-28-2008, 09:44 PM:

I need to make some modifications to an old "big red" Speco platter, but I don't know what size bit I need to use so a 1/4 inch bolt will easily thread in without using a nut on the opposite side. Any suggestions?

Any while I'm on the topic, what modifications have you made on older Speco platters (if any)?

Posted by Brad Miller (Member # 2) on 11-28-2008, 10:27 PM:

I always used thread-serts. You drill a hole in the tree and these pop into place with a small tool. They are what Christie uses in their platters.

*Mount a film cleaning bracket.
*Get longer roller bolts, such that the film is an extra 35mm away from the tree so when static electricity hits, the film isn't dragged up against the tree during payout.
*Put keeper rollers on all rollers.
*Depending on the model, upgrade the takeup roller chain.

Posted by Jeremy Weigel (Member # 4208) on 11-28-2008, 10:46 PM:

quote: Brad Miller
*Put keeper rollers on all rollers.

Did this a few months back on the payout side of our Strong platters.

Posted by John Hawkinson (Member # 1135) on 11-29-2008, 03:28 PM:

Hmm. At the risk of giving you enough rope to hang yourself:

The standard tap drill for a 1/4-20" hole is a #7, which gives 70% thread engagement. It's also reasonable to use a #9, #8, or 13/64" drill, which give 77%, 73%, or 66%.

You, of course, need to follow the drill with a tap, which will cut the threads. And use plenty of cutting fluid (oil).

If you've never done this before (like it sounds), try to find someone who has, or at the least, practice on a piece of scrap metal (stick with aluminum, not steel, unless you're really going to be doing this in steel; aluminum is much easier to work with).

--jhawk

Posted by Dave Macaulay (Member # 813) on 11-30-2008, 12:53 AM:

There is a problem with tapping the tree for 1/4" bolts - using the UNC standard 20 threads pre inch you only have a couple of threads in the metal, which (as I recall) is only about 1/8" thick. Strong uses UNF 1/4-28 bolts on just about everything in their platters, and it's a better choice for anything on the tree. The threaded inserts are the best approach though.
Be really careful about wires inside the thing. Replacing any that are damaged by drilling is definitely a non-fun activity. Make sure there aren't any hanging right where you're drilling, and a drill stop to keep the bit from going much past the metal depth is a good idea.

Posted by Steve Guttag (Member # 268) on 11-30-2008, 11:02 AM:

Christie also is a user of 1/4-28 hardware. However, SPECO has traditionally just tapped the tree for their hardware. We have some platters in service for 3-decades or more of SPECO/DITMCO and never a problem with threads ripping out.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 11-30-2008, 03:13 PM:

I've had more trouble with the alumnium inserts comming loose or competely out than with platter colum threads stripping out. The main thing is to have sufficient threads in any hole you tap. You can look that spec up in "Machinerys Handbook"

Mark

Posted by John Hawkinson (Member # 1135) on 11-30-2008, 09:18 PM:

Umm, aren't pretty much all threaded inserts steel (or stainless steel)?

--jhawk