Ratchet vs Friction Thimble

I am just curious witch one you guys find better or more accurate ratchet or friction thimble. I am going to buy a new set of Starrett No. 436 and want to know the pros and cons of each.

Thanks

Matt

This was discussed at great length,and debate several months ago,if you can search for it.

436

Hey Matt I have always found my 436 frictions to be very repeatable I used to have a grinding shop and found the friction thimbles to be almost as good as my Etalon and Mahr indicating mics. We ground +- .0001 all day every day. How can a tool that uses impulsive load ratchet be repeatable like constant friction?


My 2cents

Matt

friction thimble is nice, but i have ratchet stop.

the idea with ratchet stop is to feel your high points on turned pieces, and on flat pieces feel a contact... and only ratchet maybe twice. i've had people try and tell me you're supposed to RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET... Try and feel what you're measureing if you do that and you can't.

Basically it all depends waht you get comfortable using and so long as the person using them knows how to use them.

I prefer none. I find better measurement using my own feel instead of an interface like friction or ratchet.

It makes no difference which one you use as long as you use the same mic to measure the job to completion. What you are looking for is the same pressure on the work piece each time. If you use a mic without friction or ratchet you have to depend on you feel being the same each time and that is nearly imposible.

Carl Darnell said:

It makes no difference which one you use as long as you use the same mic to measure the job to completion. What you are looking for is the same pressure on the work piece each time.

Click to expand...

My addition to that would be to adjust the micrometer against a set of gauge blocks. That way the measurement will be good at the force that the ratchet/friction thimble/fingers produce. Works for me and mine

Ratchet or friction

I don't use either one. I don't want the mic to do my thinking for me. I prefer my own feel & will get repeatability easily within a tenth. With the ratchet & friction thimble, the more you turn it the tighter it gets & you can possibly spring back a tenth

Slapstick said:

friction thimble is nice, but i have ratchet stop.

the idea with ratchet stop is to feel your high points on turned pieces, and on flat pieces feel a contact... and only ratchet maybe twice. i've had people try and tell me you're supposed to RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET RATCHET... Try and feel what you're measureing if you do that and you can't.

Basically it all depends waht you get comfortable using and so long as the person using them knows how to use them.

Click to expand...

That's funny, but true with the newbies learning to measure. I suspect they think it is a torque wrench, and the more they crank, the more accurate the measurement will be

What I don't like about friction thimbles is that the break-away torque may or may not be consistent between mics. Ratchet is pretty repeatable because they tend to click at a fairly light engagement, IMO anyway. Also, the small diameter of the ratchet knob makes a good speeder to move the mic across large ranges quickly, compared to plodding along with the friction thimble which is the full size of the barrel....at least in the few friction mics I have tried (Fowler electronic).

Somewhere around 15 years ago I was a member of a design and manufacturing team tasked with developing a method to mount a 6-footed weather camera on a spacecraft structure without straining the camera more than the 0.0002 inch over the camera's roughly 2 ft x 4 ft base, which the camera maker said was necessary to prevent degrading the camera's performance.

We designed and built a "strongback" fixture that hard-mounted to 3 of the spacecraft structure's mounting points, and used micrometer heads to measure the heights / depths of the other 3 points relative to the plane defined by the hard-mounted points. But when we did our validation testing, we found that the 3-sigma measurement uncertainty was very nearly 0.0004 inch.

Eventually we traced the micrometer errors to click-to-click variation in the micrometer ratchets that could only be controlled by a controlled-rate clicking through one full revolution of the ratchet stop. Eight clicks at one click per second for Micrometer 1, then Micrometer 2 and finally Micrometer 3 was the magic needed to reduce the 3 sigma measurement variability to less than 0.0001 inch.

We celebrated only after the camera's measured-in-orbit performance exceeded our customer's expectations.