comparator shopping....which options are must have?

We are a little green when it comes to specifics on comparators and I was wondering if you guys could help out and tell me what you would consider to be a must have option. We are looking for a used comparator in the 14" size range.

Here are some specifics of one we are looking at:
Mitutoyo PH3500 new in 1999
Horizontal travel 10"
vertical travel 6"
table swivel +/- 10 degrees
single lens mount

Equipped with:
micropak 2 axis computational readout
digital andle display
dual fiberoptic surface reflection
1 lens- 10x

Thanks for your help!
Matt

First question I would ask is how much $$$ are you budgeting for this? I have used comparators that had little more than micrometer heads to measure table movement to DRO's that would let you line up the crosshairs on the screen, hit the "Enter", and would calculate bolt circles, angles, etc. Next question: what kind of tolerances are you dealing with?

We are in the 7k -10k range. We prefer to have readouts on them. For what little I have used one it seems to be a must.

Tolerances aren't really tight. +/-.002 would cover most everything, but I would prefer that the machine be capable of measuring closer than that.

MITUTOYO 14" PH-3500 OPTICAL PROFILE PROJECTOR COMPARATOR FOR SALE & UNDER POWER - YouTube

I don't know the company or what it'd cost. Looks good to me. Maybe you can find out what that one sold for as it's probably long gone?

I do not think a 10X lenses will give you the repeatability you need for +-.002"
would recommend using a 20X at a min for this type of accuracy

If you do get this machine will they give you a traceable certificate of conformance for repeatability accuracy and traceable to validate and qualify the machine?

From J&L Metrology website
" A basic rule of thumb is that a typical attentive operator can repeatedly discriminate .004” on the comparator screen. Dividing the “discernible resolution” by the lens magnification determines the minimum resolution attainable for each lens"

By this standard, and this was how I was trained to select my measuring tool, you only have a repeatability to .0004" even a 20 power is marginal at .0002". My past employer we used an old J&L that had a 32.5 and 50 X in addition to the 10 and 20. I would have been using 32.5 or the 50 for a +-.002". today I have DCC and manual OGP machines with variable resolution available as my options for tight tolerance features. Just my 2 cents for what it is worth.

masome said:

We are in the 7k -10k range. We prefer to have readouts on them. For what little I have used one it seems to be a must.

Tolerances aren't really tight. +/-.002 would cover most everything, but I would prefer that the machine be capable of measuring closer than that.

Click to expand...

Readout is a must have.
One that does radius size calculations is very nice to have.
Auto edge detect is nice but would be way down my list.

As mentioned a 10x lens is a bit light for .002 work and new lenses are not cheap but Mits makes some of the best.
The only downside that I've seen on this machine is that the stage is a bit wimpy.
Bob
.

There are 3 different comparators in use where I work.
The one I like to use (a J&L) has a vernier ring around the screen...the other 2 have an angular DRO.
Maybe it's just me, but I have more confidence in the vernier for measuring angles.



Rex

bjorn toulouse said:

The one I like to use (a J&L) has a vernier ring around the screen...the other 2 have an angular DRO.
Maybe it's just me, but I have more confidence in the vernier for measuring angles.

Click to expand...

I think it has a lot to do with what you learned originally.

My apprenticeship (and previous experience) was entirely mechanical.
DROs didn't exist then, so I'm more comfortable with mechanical measuring instruments.

But state-of-the-art DROs can give readings that are orders of magnitude more accurate than mechanical systems.

- Leigh

Great feedback. This is what I am looking for. What can one expect to pay for different lenses?

I am probably going to buy this comparator from the same faciltiy I have bought my VMCs through. They repair and recalibrate the comparators.

We are also looking at a Deltronic comparator that has there most basic DRO on it. It does have the edge detection. It can calculate a 3 point radius....The mitutoyo seems to have better functionality when it comes to the DRO...Would the edge detection on the Deltronic beat out the extra functionality of the Mitutoyo?

Not sure of current lens price.
I'd expect $600-$1000 for a 50X.
Lower mags are cheaper, last one I bought was $2950 but it was a 200x for a different brand machine and quite a while ago.
They are not cheap but quality optics are what make these things work.

In general I don't like auto edge detectors as most mount on the front of the screen and get in your way.
Some people I know love them.
Way up the price scale you get into comparators with machine vision buried into the guts for edge detect. These are just plain sweet.

Just an opinion but I'd buy a Mits over a Deltronic. IMO not even in the same class.

Stage size to handle your parts is a big factor in some cases. You are not going to put V-8 crankshafts on either of these machines.
On larger OD round parts (like checking the form on a 6 inch grinding wheel),"lens standoff" can be a factor.
If you need it, surface illumination quality varies a lot over different machines and goes downhill fast at higher mags. Don't be fooled by a demo at 10x.
Digital protractors are nice but they read beyond the capability of any tech to align the screen with the center of rotation.
Very useful if you need the readout to spit SPC data to a computer for you so you don't have to type the number in.

You really should take some of your parts and try them out on the machines that you are looking at.

Bob
(I know just enough about these machines to be very dangerous so take my words with caution. I have owned four PH-3500s and overall I was very happy with them.)