Squareness comparator’s bumpers

[Gareth JeffersonParticipant @garethjefferson65077]

Please put me right (nicely) if I’m in the wrong forum with this question.

All the squareness comparator designs I’ve seen, mostly on YouTube, have had a curved “bumper” at the front edge of the base. I’ve never seen an explanation of what purpose this serves. Is the radius of the curve critical, and if so why (my maths is about a rusty A level, if that helps.

I’ve done lots of Google searches but to no avail so far.

Either an explanation, or a link to something relevant would be greatly appreciated.

— Gareth.

[Gareth JeffersonParticipant @garethjefferson65077]

[HopperParticipant @hopper]

No the radius is not critical. Some have a large radius, others use the ball turned on the bottom of the vertical rod on a standard marking out gauge, so about 10mm diameter. You have to have some kind of radius to use the comparator. You kind of roll the base around the radius and the reading is the minimum shown on the dial gauge. That way you are comparing one point at the bottom with the one point where the dial gauge plunger contacts. If the bottom 'bumper' were a straight line, you would be comparing the whole line across the bottom with the one point of the DTI plunger, which could introduce errors if the piece being tested were not perfectly flat all the way across the base.

[Brian WoodParticipant @brianwood45127]

Hello Hopper,

One learns something every day, thank you for the lucid explanation.

Regards

Brian

[SteveIParticipant @stevei]

Gareth,

 

Are you thinking of making your own or looking to understand what is important to aid in buying?

 

Hopper is of course bang on the money. One issue I have found is that if you are trying to check squareness to very tight tolerances then the you need a tool that repeats the measurement reliably. Otherwise it will drive you mad. Obviously you are looking to compare squareness but what in terms of job are you looking to do with it?

 

A standard marking out gauge can do a really good job but the units which are especially made for this type of job are very heavily built i.e. rigid when compared to a standard marking out gauge. The marking out gauges have more degrees of freedom which the comparator does not need. When you are using a tenths/50 millionths/micron dial indicator you need all the stability, rigidity you can get. You will also need a reference to calibrate the comparator to. The classical method is to use a cylindrical square but the cheapish granite tri squares from china are more than good enough.

 

Stefan Gotteswinter has a video on youtube about making a squareness comparator and oxtool has a few examples of using one.

 

Steve

Edited By SteveI on 18/02/2018 16:31:53

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