gear profile checking

[tomtomtom]

hi, i have acquired a second hand brown and sharpe (non CNC) with pd-dmis, i am just getting to grips with it and have had no training so am a little stuck. i'm trying to get the profile of an odd gear so that i can export the dxf and wire erode the new gear straight from that. when constructing the curve i'm doing it one point at a time and then creating a curve from those individual points, however i am getting some strange results in the way of points that dont lie where i'd expect them to, resulting in strange curves as opposed to the normal involute form i was expecting. i dont think its my bad hitting as i've tried doing it a few times but it could be! any tips would be appreciated!!
also, stupid question but how do you simply find the diameter of a circle?!?! i can define and construct the circle but under 'dimension' there's no diameter function? what have i missed?

thanks in advance, any help would be appreciated!

tom cresswell

[Matthew D. Hoedeman]

hi, i have acquired a second hand brown and sharpe (non CNC) with pd-dmis, i am just getting to grips with it and have had no training so am a little stuck. i'm trying to get the profile of an odd gear so that i can export the dxf and wire erode the new gear straight from that. when constructing the curve i'm doing it one point at a time and then creating a curve from those individual points, however i am getting some strange results in the way of points that dont lie where i'd expect them to, resulting in strange curves as opposed to the normal involute form i was expecting. i dont think its my bad hitting as i've tried doing it a few times but it could be! any tips would be appreciated!!
also, stupid question but how do you simply find the diameter of a circle?!?! i can define and construct the circle but under 'dimension' there's no diameter function? what have i missed?

thanks in advance, any help would be appreciated!

tom cresswell

Ok, first off, Pcdmis will ONLY ever comp in 2-D for a touch-trigger-probe scan. A laser scan or continuous contact scanning head, it will do 3-D, BUT, never with a TTP. So, the first thing I would do is TURN OFF the probe comp. Then, once all the data is scanned and you make the curves (NOT in Pcdmis, do it in a CAD package), offset by the calibrated probe radius.

As for the diameter, if you have either a mesured circle or a constructed circle (measured is better), simply report the D axis.

[Cumofo]

The circle diameter evaluation is under the "location" icon.
I don't think you will be very successful generating a full gear profile with a manual CMM, but you can give a qualified CAD operator all he needs to fully develope the geometry needed for manufacturing.
Do your best to measure the root diameters of what you need, and some of the lead in and out ramps.
Translate all the features to the same plane to give the "profile" a finished look, and export it to an igs. A step file might not read out all the splines.



G

p.s.

Also check the ansi spec for similar gears, it will help you to understand what information you need to pass on to your CAD operator/ Engineer.

[Wes Cisco]

Hello Tomtomtom,

Welcome to Pc-Demon!
If you select location from the dimension menu diameter is an option, it is in the second column of tick boxes labled "D". If you are reporting trueposition it will be labled "DF".

There is a special "module" of pc-dmis for gears and a seperate section of this forum just for that module and gears. I am not saying you can't or shouldn't post on the main CMM board, I am just trying to help you find the information you need.

Now these points you are taking, are you using vector points? Do you know what the vectors should be? Are you in the proper workplane when you do your constructions? These are the things that occur to me that could be the problem.

[tomtomtom]

ok thanks for that, i'm still getting the problem though with the anomolous points. i have tried moving the probe by hand and have tried locking the axes and using the X and Y wheels but obviously it is difficult to get every hit nearly perpendicular to the gear profile, could this be my problem? i dont know how careful to be.

thanks for the diameter solution, this site was a lucky find!

[Matthew D. Hoedeman]

ok thanks for that, i'm still getting the problem though with the anomolous points. i have tried moving the probe by hand and have tried locking the axes and using the X and Y wheels but obviously it is difficult to get every hit nearly perpendicular to the gear profile, could this be my problem? i dont know how careful to be.

thanks for the diameter solution, this site was a lucky find!

That is why you turn OFF the probe comp, then you offset the end data by the probe radius. You will never get correct probe comp, so don't use it, put it in later.

[tomtomtom]

"The circle diameter evaluation is under the "location" icon.
I don't think you will be very successful generating a full gear profile with a manual CMM, but you can give a qualified CAD operator all he needs to fully develope the geometry needed for manufacturing.
Do your best to measure the root diameters of what you need, and some of the lead in and out ramps.
Translate all the features to the same plane to give the "profile" a finished look, and export it to an igs. A step file might not read out all the splines."

cheers for the advice thats what i plan to do. get the info of the curve export into cad to tidy it up and make it a true-ish 2d profile for the wire. as yet i havent come up with a curve i want to trust!! this is a ground gear as well so with a 3mm ball probe the anomolies cant be put down to surface finish.

thanks again for your quick responses

[tomtomtom]

Ok, first off, Pcdmis will ONLY ever comp in 2-D for a touch-trigger-probe scan. A laser scan or continuous contact scanning head, it will do 3-D, BUT, never with a TTP. So, the first thing I would do is TURN OFF the probe comp. Then, once all the data is scanned and you make the curves (NOT in Pcdmis, do it in a CAD package), offset by the calibrated probe radius.

As for the diameter, if you have either a mesured circle or a constructed circle (measured is better), simply report the D axis.

to get rid of probe compensation do i just go to PROBE/EDIT and then change the calibrated diameter (2.99) to 0? or is there a button with probe comp ON/OFF?

cheers

[T Miller]

Edit prefs/probing turn off there