Interapid Indicator Repair Manual
“Did you tighten the screw?”
My father and I worked side by side for 31 years. He repaired calipers and I repaired indicators. He taught me everything he knew, which was a lot. During the 1960s and 70s he had been service manager for the company which imported the Interapid indicators from Switzerland. He had been sent to the factory for training on several occasions.
When he started Long Island Indicator Service we began working out of the basement in our home.
The two of us sat silently at our work benches for three hours every morning. All you heard was the occasional tap-tap-tap of the small metal hammer. At noon, my mother would call us to lunch and then we’d converse and discuss business and make plans. English was not his first language but he became a good conversationalist and easily entertained anyone willing to listen. After lunch we’d silently return to our work benches.
He did not teach me the Interapid indicators right away. They were difficult and because he said so, I approached them nervously. Now, 45 years later, I don’t see what the problem was but that comes with experience.
He must have noticed that I was spending a lot of time on one particular gage one day but nothing was said. I tried everything I could think of: Replaced the hair spring; cleaned the ball bearings once again; de-magnetized; etc., etc. Although it was quiet, I’m sure he heard a bit of exasperation in my sighs. Without looking up, he quietly asked, “Did you tighten the screw?”
Sometimes it is the obvious that gets overlooked.
My father is no longer here to add his two-cents’ worth. There are many times I wish he were. I can only say that I am grateful for his calm demeanor, genuine efforts, and good humor which all contributed to making this such a satisfying profession for me.
René Urs Meyer, Long Island, New York
Can it be repaired?
Your primary consideration should be: Can you get spare parts? In theory, any Brown & Sharpe distributor should be able to provide you with parts for current models. In practice, almost none of them will have parts in stock and they would have to send for them. This is time consuming and costly for them. Selling a $5 spare part can cost them many times that amount in shipping and processing fees. They may not want to co-operate. You should be prepared to place a substantial order to make it worth their while.
Some websites, such as www.longislandindicator.com may offer parts for online purchase but you must also expect to pay more than published list price. If you can’t get parts, there is no sense in trying to repair a damaged Interapid indicator.
Check to see if it is repairable before you begin investing time and money in your repair project. This is easily the first step, yet how many times a year do I wish I had followed this admonition?
Look carefully at the front end. If it is squashed out of shape or the ball bearings  can no longer be properly inserted or removed, you will have to replace the indicator body. This is expensive and may not be worth while.
If the dovetails are damaged (they may have been ripped off) check to make sure you can remove any screws that may be stuck in the threads and that it will be possible to install new screws. The indicator can still be fastened by the 4 mm diameter stem if the dovetails become unusable. Otherwise, you will also have to replace the body.
If the 4 mm diameter holding stem is broken, it can be replaced as long as the body is not damaged at that end.
It may look impossible but if the entire movement is broken off it can usually be repaired. This will understandably require more parts than normal.
It may be possible to repair old models, those of the 310 and 311 series which were produced before 1980 (a rough estimate), but you must take into account that spare parts are no longer commercially available.
If you are not yet familiar with all the Interapid models, their ranges, their dial diameters, their contact point sizes, their accuracies and current availability, take a close look at the information on the Long Island Indicator Service web page, the TESA catalog published by the manufacturer, or keep a copy of The Companion Reference Book on Dial and Test Indicators close to hand.
Problems with the new plastic dials
Spanner nut and ball bearing
Special spanner wrenches make the work easy, but these are not available. For best results, use needle nose pliers and a screw driver that fits the slot perfectly.
Hair spring and gear assembly
Hair spring identification
.0005" (123092) on left and .0001" (123100) on right
A note about the -15 and -15V model hair springs
These indicators use a unique hair spring to counter balance the weight of the extra long contact point. The crown gear pre-load should be 3/4 of a turn. Even then, you may encounter some slight jumpiness in the dial hand, especially when compared to the standard models. We have not found a good way to avoid this. You will also see that repeatability is less than ideal. You can count on about 1/2 graduation. Taking the length of the point into consideration, you can easily see why this would happen. Use these models only if you have no other option.
Minor adjustments are not a good idea because…
Interapid indicators fit together like a puzzle. If you try to adjust one piece, the rest goes wacky. For instance, you may be tempted to remove the movement (the dial assembly) which is fixed onto the body with two black screws easily visible on the underside. If you take these screws out then you won't be able to get the indicator back together in working order, unless you know what you're doing of course.
Similarly, your indicator will have four or six ball bearings. Very small amounts of tightening or loosening can be accomplished but do not remove any of these bearings or loosen them to any significant degree. Again, you won't be able to put Humpty Dumpty together again.
If you really want to adjust or repair the Interapid indicator we strongly suggest getting the repair manual to help you along.
Corrections and additions to the Repair Manual (2016 edition)
Q: I have relatively new indicators that work fine but the calibration lab says they are off by as much as .03 to .05 mm per revolution. Do they need to be repaired?
Q: I have an Interapid indicator that has a little play side to side with the end. It will repeat fine as long as you don't move side to side on the part you're indicating. I was wondering if you could give me some advice on what I can do to fix the play?
Q: My indicator works fine but when I swivel the contact point, the hand moves off to the side and no longer points to 12 o'clock.
Additional information on the Interapid Test Indicator can be found on the following pages: