Bore Measurement Again
OK, so instead of hobby jobs a paying job comes into my home shop. I have several hubs that have to be bored for bearing races for tapered roller bearings.
Measuring bores with extreme accuracy has been trying at times and if possible, I make a shaft first, then fit the bore to it, using is as a gauge. This is OK for running and light push fits but for press fits falls short because I can't tell how much smaller the hole is than the shaft. In any case, that method won't work for me on this job.
So, I'm faced with a few choices. I can try to use my inside caliper or snap gauges which thus far haven't proven to produce extreme repeatable accuracy, or I can try Oldtiffe's "Stick Method" mentioned in a previous thread and also described in Guy Lautard's books, I can purchase a Bore Micrometer or Dial Bore Gauge set which just happens to be on sale at Enco right now with free shipping. I've also considered making a "go gauge" turned carefully on the lathe to fit the bore when it reaches a size for a "light press fit" as described in South Bend's How to Run a Lathe and "sneaking up" on the diameter of the bore with the compound offset about 84 degrees which would prove quite time consuming because no actual amount of material to be removed is known. It would also require the manufacture of two "go gauges" because I have two different bore dimensions. Further, I have no Tool Post Grinder available so grinding the gauge isn't possible, it would have to be turned with a fine finish and perhaps polished with emery cloth & oil.
I believe accuracy within .0005" would be sufficient for this project. I would appreciate any thoughts on which method I should use before I get started. I don't mind purchasing the Dial Bore Gauge, if it will do the job. Owning good tools that work is always a good investment in my opinion. On the other hand, I don't want a "gadget" that isn't any better than what I already have. The thought here is to obtain the required precision with the least effort and time investment.
Thanks for taking time to respond.
Last edited by firbikrhd1; 01-13-2010 at 07:18 PM.
What is the diameter of the bore and what class of fit is required?
A lot of this data will be in the bearing manufacturers or distributors web site.
If you can't find the data or tolerances, post the nominal diameter and class of fit.
I will be surprised if your limits are closer than 0.001" or 0.0005"
"Class of finish" is just as important as class of fit as the "tops" of a comparatively rough finish will obviously not to the job as well as a better finish at the same size.
Are you going to press the bearings in - or not? There is a good reason for my asking as the class of fit had a limit range that is from the largest bearing in the smallest hole (tightest) to the smallest bearing in the largest hole (least tight). If the bearings exist and/or you have them and can measure them accurately you can use the "unused" limit from the bearing and use the over-all limits instead of just those that apply only to the bore and so have a wider tolerance with an easier job foe the same end resultant class of fit.
The "stick" method WILL work. All or any others are only variations of it - bore micrometers, inside micrometers etc. etc.
As you say, boring accurately is much harder than turning an outside diameter to the same limits.
For those not aware of what the "stick" method is - here it is:
In my (limited) experience the dial bore gauges are good for measuring taper in a bore but are hard to use to measure accurately the diameter, you have to set them with a mike or standard first...I wouldn't try to use mine to measure to half a thou. The inside mikes, however, work nice. CDCO also has inside mikes, and inside sets with interchangable rods, that are reasonably priced and (my copies, anyway) measure with good accuracy... // video_man
It wasn't clear if you have some of these, which don't cost an arm and a leg and should get you to 0.001" if not better. Of course, you'll need a good mic to measure them with.
I'm partial to real inside micrometers. Like an outside mic, but has jaws that fit the inside of the bore. They provide the same feel as a standard mic, and come with setting rings.
Page 629 top of page.
I have models sold by CDCO.
Search for SKU 32101, much cheaper, but for the occasional use, they work fine for me.
If I checked, with a good outside mic and standards, readings to within a tenth are very probable.
You said they are taper bearing races and those races are not critical to bore dimensions like a ball bearing is.
Don't try to use a dial indicator bore mic on a bearing race bore because the bore is not long enough to get a good reading.
Inside mic's or telescopic mic's are the way to go. For the taper bearing race a telescopic mic will get you in the tolerance you need. For closer work use the bore mic.
When I use a bore mic I get the bore mic set to the hole and then use outside mic's to get what the bore is. The reason is it's easier to calibrate an outside mic than it is a bore mic.
When I do a bore for a bearing I use telescopic gages to get within .010" or so and then start using a bore mic for the final size I want. Sometimes I use a flapper sanding wheel in a die grinder to finish the bore to size and smoothness, just leave about .0005" to .001" to polish out to size.
What ever you do don't depend on dial calipers, digital calipers or telescopic gages to get to the finish size. Use mic's.
It's only ink and paper
Telescopic Gauges and Knowing how to use them will enrichen youre Machining Career. I have used mine to super close bore tolerances many times . They are the best thing to use for youre Job.
I hate snap gauges... and I do know how to use them... Good for getting "close", but I don't rely on them for "exact". I have a nice bore gauge that gets me "in the zone" also.
And.. If I really need to know... I have many sets of gauge pins.... 3 pins and you can measure a "diameter" very nicely. Boring without a taper - that's another issue to keep an eye on.
For super precision bores, without expensive bore gages, I prefer
to use an adjustable Parrallel and two dowel pins.
put the pins on top and bottom of the bore and the parrallel inbetween.
Slide it until the feel is snug, and lock the scew on the parallel so the setting is kept.
withdraw and mike the assembly at the bench.
Because you are using the pins on the surface exposed to the bearing races (later) surface finish issues are nullified
Super acccurate for few $$
Last edited by Rich Carlstedt; 01-13-2010 at 10:18 PM.
Rich, that's a great idea. All you have to do is measure the adjustable parallel and add the diameter of the two pins to get the bore size.
That's an interesting trick.
It's only ink and paper