Film-Tech Forum ARCHIVE: I need the inside diameter of a 70.6mm lens collar.

This is topic I need the inside diameter of a 70.6mm lens collar. in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Alan Gouger (Member # 543) on 09-18-2009, 02:38 PM:

Im having a sleeve made for a projector which will take a standard 70.6mm lens. What would the inside opening of the collar have to be to comfortably take a 70.6mm lens without allowing to much play. This will be a fixed adapter so no screw to tighten it down the lens will simply slide in and out.

Thank you.

Posted by Alan Gouger (Member # 543) on 09-19-2009, 11:22 AM:

Just in case I did not word this very well. I had a machine shop bore out a sleeve for a 70.6mm lens and it was to tight. Lens do not fit. He is asking me right down thousands of an inch what the diameter needs to be. I do not own any calibers and have no way to precision measure myself. If anyone can help Id be grateful.

Thanks guys.

Posted by Tony Bandiera Jr (Member # 2365) on 09-19-2009, 12:35 PM:

Alan, you need to actually measure the bore of the particular machine you're trying to get this lens adapter into. Anyone of us here could give you a measurement of one of our machines down to 1/10,000th of an inch, but it would only work for the machine we measured it on.

So talk really nice to that machinist and ask him to travel to your site and take that measurement for you. Perhaps offer to buy lunch or see if he would charge only a modest fee.

By the way, even if you had the calipers, measuring a bore diameter accurately takes skill and patience. It is way too easy to get an inaccurate measurement.

Any fee you may have to pay the machinist to travel to you is very likely to be far less than the repeated fees to keep re-machining that adapter!

By the way, what make and model is that projector? I am not aware of ANY make that does not have a clamping screw to tighten the adapter in with.

Posted by Sam D. Chavez (Member # 1841) on 09-19-2009, 12:38 PM:

You need to take him a lens or two so he can measure them and then ream out the inner diameter. Lenses vary a bit in this regard as do the sleeves.

I'm assuming you mean the lens won't fit into the lens adaptor.

Posted by Tony Bandiera Jr (Member # 2365) on 09-19-2009, 12:45 PM:

Good catch Sam. [thumbsup]

Even the lenses would vary ever so slightly in diameter, would they not? I'm not sure what the tolerances of a len's O.D. are and since it sounds like Alan wants a "force fit" with no setscrews, seems to me he'll need a collar custom machined to EACH lens.

Wow.

Posted by Alan Gouger (Member # 543) on 09-19-2009, 01:10 PM:

Hi Tony

Thanks for your attention to this. A little more detail. I had a custom lens barrel manufactured to allow the use of a standard 70.6 mm cinema lens with our DLP projector. This was done to allow for longer throws. Projector brand not important.
Everything works great with test jig. Everything has been done except for the final bore to accept the lens. The machine shop is on the other side of the country so they are not on hand to measure themselves and gave me something larger then the 70.6.
On their first try none of my lens fit. We do not want to go to big giving us to much slack preferring just enough to allow the lens to slide in and out without a lot of effort and force.
When they say the lens is a 70.6mm lens how accurate is that number? I could send them a lens but we are short on time and have a demo this week so sending a lens is no longer an option which is why Im pinging anyone here hoping I can get a someone to provide the accurate measurement needed.

Thanks.

Edit: Hi Sam looks like we were posting at the same time. From your answer looks like the 70.6mm is not a no tolerance spec. If variation is common then I will pass that information along. Maybe I will order a few adapters one larger then the other for those lens needing more room. This is the answer I was looking for, thanks to both for your help!!!

Posted by Demetris Thoupis (Member # 833) on 09-19-2009, 01:26 PM:

If I were you I would make the trip to have it done right and see that its right. It's your best option than waiting to see if what they send is right!
Demetris

Posted by John Hawkinson (Member # 1135) on 09-19-2009, 01:42 PM:

The tolerance from an interference fit to a press fit to a slip fit can be as low as 0.002"; at that point you should really take some 120-grit sandpaper and just sand down the inside of the sleeve until it fits comfortably. You shouldn't have any trouble shaving off 0.0001" in a few seconds, assuming this is brass or aluminum.

ALSO: Do yourself a favor and buy yourself a caliper. Harbor Freight sells el cheapo CEN-TECH chinese import calipers but their quality is fine, they're good to 0.001" or so (they read to 0.0005"). Last I looked they were on sale for $12 or something, but now they're up to $19.99. But either way, a must have.

--jhawk

Posted by Alan Gouger (Member # 543) on 09-19-2009, 02:09 PM:

John just ordered a pair of Calipers. Good advice!

The sleeve is aluminum. Ill give it a little elbow grease and see what happens. Thx.

Posted by Louis Bornwasser (Member # 3063) on 09-19-2009, 03:47 PM:

In Rochester, call Dave Claussen at ASP industries 254-9130. He is very good. If he cannot help, have him reccomend a place for which you can go. (No, not THAT one.) Louis

Posted by John Walsh (Member # 168) on 09-19-2009, 05:12 PM:

SMPTE has a standard for projection lenses and mounting (ANSI/SMPTE 243M-1993) (not available on freely online) which shows suggested tolerances for manufacturers. Also, there are 'classes of fit' where how tightly one part slide into another is defined:

(I tried to create a link to the Machinery's Handbook defining fit, but the ubb code is not working, but anyone can look that up.)

With these two documents, you should have enough to get an idea of what to make.

Usually, everyone just buys a collar, but I'm assuming you have a special application where a custom collar is required. Most (not all) collars have a split on them which allows the collar to be opened (or closed) a little so an exact fit isn't required