# How to measure hole when boring between centres?



## SignalFailure (Dec 14, 2009)

Basic question I'm sure and the title sums it up but how does one measure the diameter of a hole when boring between centres without removing the boring bar?

TIA

Paul


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## rklopp (Dec 14, 2009)

Maybe I'm dumb, but I've never succeeded in boring while work was held between centers. I've always found the center is in the way, no matter where I put the tailstock. 

Explain what you mean.


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## Metal Butcher (Dec 14, 2009)

Paul  said:
			
		

> Basic question I'm sure and the title sums it up but how does one measure the diameter of a hole when boring between centres without removing the boring bar?
> 
> TIA
> 
> Paul



I don't see any reason the boring bar can't be removed to take a measurement. I don't do any boring using this method, so maybe I'm missing something.

I'm sure someone with more experience will be along to shed a little more light on this subject.

-MB


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## Jasonb (Dec 14, 2009)

Paul means holding the part on the cross slide and using a between centres boring bar.

You will have to take the bar out as you get close to finish size, before then you may get away with using callipers. One other method is to turn a plug gauge and put a hole in it to clear the boring bar, just slid it out the way when boring then offer it upto the hole when the lathe is stopped.

Jason


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## mklotz (Dec 14, 2009)

I've never bored between centers but, if put to the task, I would do as Jason suggests with one slight modification. I would taper the plug gauge so that I could use it to determine how much more I needed to take off by measuring its penetration into the developing bore.


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## phlegmatic (Dec 14, 2009)

Never did this either, but if the hole is big enough perhaps it can be possible to hold reference peices wiith toolclamps on the inside of the bore, and then use an outside mike? Just a thought!


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## SignalFailure (Dec 14, 2009)

Thanks everyone for the suggestions, the sliding tapered plug seems to be the way to go (why didn't I think of that?!) and given sufficient diamters of the two ends it could be used for bores of a range of sizes I suppose.

Thanks again, I'll post on my success or otherwise in due course (it's for the next project  )

Paul


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## tel (Dec 14, 2009)

My, admittedly limited, experience with this method leads me to believe that the 'sliding plug' method would be unreliable at best. The problem is you need the heftiest possible bar for any given bore and the slotted plug would be a sort of 'C' shape with walls too thin to guarantee there would be no spring when measuring. Probably be OK in the larger bores, where the relative thicknesses would leave enough wall thickness but to (say) bore a hole of 5/8" diameter, one needs a bar approaching 1/2" dia, which makes the plug pretty fragile for the purpose.

With between centres boring, the bar is usually removed to make the measurement, by the very nature of things, it will return to exactly the same position when it is replaced to resume work.


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## SignalFailure (Dec 14, 2009)

tel  said:
			
		

> With between centres boring, the bar is usually removed to make the measurement, by the very nature of things, it will return to exactly the same position when it is replaced to resume work.



Possibly not coming back to exactly the same position was the reason I didn't want to remove it but I hear what ya say about the plug and a stout bar....experimentation called for!


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## Jasonb (Dec 14, 2009)

I was thinking along the lines of the plug gauge being a ring not a C shape, but as you say would depend on teh bar/bore clearance


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## mklotz (Dec 14, 2009)

Tel,

I don't understand your "C shape" reference. The gauge I'm envisioning is a cylinder that's fitted on the boring bar before said bar is mounted between centers. It's free to slide on the bar and has a tapered end that slides into the bore.

Regardless, your concern is a valid one and would have to be addressed - hopefully by Paul in the photo report he's going to deliver regarding this operation. 

If nothing else, the sliding gauge could be useful until you got close to the target dimension, at which point final sizing is done by removing the boring bar as you've indicated. (Pulling the bar every time you want to check the size seems like such a pain.)


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## rake60 (Dec 14, 2009)

I would use an inside caliper myself.
_*Enco*_ has them available at reasonable prices.

Rick


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## Maryak (Dec 14, 2009)

Paul,

If you use a chuck at the headstock end to hold the bar then you can remove the tailstock, clear the bar and measure with your chosen instrument. Assuming the lathe bed is long enough for this. Otherwise like Rick I would use inside calipers and the size of the bend in the caliper tips would determine the maximum bar diameter.

Hope this helps

Best Regards
Bob


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## SignalFailure (Dec 14, 2009)

Photo report Marv? Ooops, just dropped my camera...what a shame :big:

Rick, I've got some inside calipers but they don't seem that accurate to me.

Bob, it'd have to go in the chuck as I've nothing else to grip it with 

Once the last few bits are made for the current project I'm going to make a boring table and bar and give this a shot....

Thanks again all for the help.


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## tel (Dec 14, 2009)

mklotz  said:
			
		

> Tel,
> 
> I don't understand your "C shape" reference. The gauge I'm envisioning is a cylinder that's fitted on the boring bar before said bar is mounted between centers. It's free to slide on the bar and has a tapered end that slides into the bore.
> 
> ...



Ah, OK Marv, I misunderstood what you meant - I had in mind the cylinder with one side cut away to straddle the bar. No reason your idea could not be made with one or more undersized steps, rather than the taper, as well as the finishing diameter.

'umble apologies!


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## rklopp (Dec 14, 2009)

Jasonb  said:
			
		

> Paul means holding the part on the cross slide and using a between centres boring bar.
> .........
> Jason



OOOOOHHHHH, That's what he meant. I suppose I'd measure the distance between the boring bar and bore wall on opposite sides along a diameter using small hole gauges, plug gauges, or telescoping gauges, and then add in the diameter of the boring bar as measured by a micrometer or slide caliper.


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## putputman (Dec 14, 2009)

Paul, like Maryak said, if you have a long enough bed on your lathe you should be able to back off with the tailstock, move the cartage to the right and measure the bore.

In my photo of the lathe you can see the boring bar clamped in the three jaw chuck. Once the bar is in place I do not touch the chuck until the job is done. You also notice I have an indicator on on the carriage and reading the position of the crosslide. I set that at "0". When I get to the point I want to take a measurement of the bore, I rotate the cutter towards me and then move the crosslide toward me a few thousands so the bar does not drag as i move the carriage to the right. Move the tailstock out of the way and move the carriage to the right. Take your measurement and make the adjustment to the cutter in the boring bar. Reset the tailstock and move the crosslide back to "0" make the next cut.

I make my cutter adjustments using a micrometer over the boring bar & cutter. It can be very accurate if you take your time. 

I have use this process on several engines that are too big to bore on the Bridgeport.


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## hammers-n-nails (Dec 14, 2009)

this is the first time ive heard of this method and i have a part that i will be building soon that i think this method would work very well for but what is the best way to get the part to be bored centered at the tailstock end, at the headstock end i assume you attach a DI to the faceplate and rotate the lathe, but what about the other end?


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## tel (Dec 14, 2009)

One simple way is to use centres in headstock and tailstock. If, for instance, the workpiece was a cylinder block with a cored hole you wouls plug the hole at both ends, carefully mark out the centres on the plugs, put a little pop mark in, gently open out the pops with a small centre drill and then set up from there. One you have the workpiece clamped in the right position you bore the bore and face one end before disturbing anything, these become your datum surfaces. Mark the faced end, as this one will be really true to the bore, and is the one you want to make the 'working' end.


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## hammers-n-nails (Dec 14, 2009)

thanks for the quick reply tel, and sorry for getting a little of topic everyone. to be more specific i am going to be building the crosshead guide for this engine http://www.homemodelenginemachinist.com/index.php?topic=6512.0 unfortunatly you cant see the part in question in any of the pics i have but i will try to describe it. it consists of a 5 3/4" od x 4 5/8 id x about 22" long inside of which will be the two guides, plates also concave on the same center with an id of 4 1/2", most of the outside is cut out and all but a small part of the crank end will be cut off, when i cut this off and weld a bunch of other stuff on such as mounting brackets and the crankshaft bearing carrier i expect the tube will warp considerably so i need to do the turning as the very last step. my point is that i wont be able to get the tailstock up close to any part of the tube that is still mostly there. i will probably be using this lathe(the other one is only 40" between centers) if that makes any difference http://www.homemodelenginemachinist.com/index.php?topic=6233.0 . any thoughts on aligning or details of the boring bar i should construct, i was thinking of using a piece of pipe say.... 3 - 3 1/2" od and attaching a pice of tool with a setscrew behind it for adjustment and a couple locking screws? thanks


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## joeby (Dec 14, 2009)

You can, assuming the boring bar is already mounted between centers, clamp your DTI to the boring bar on either end. This will allow you to indicate on each end of the bore, by rotating the chuck, to get your part centered. I have a few small horseshoe magnets with short posts epoxied to them that work well for attaching the indicator to the boring bar.

 A length of heavy walled pipe may work for a boring bar, but chatter may be a problem. It would certainly be easy enough to plug the end(s) and centerdrill them for use between centers, and possibly a donut shaped toolholder to slide over the pipe and be clamped into position. An added bonus would be the ability to position the tool anywhere along the length of the bar to suit the job at hand.

Kevin


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## Jasonb (Dec 15, 2009)

I'll dig out some pictures of large traction engine trunk guides & cylinders being machined for you when I get back in from work.

Though if you are welding all the bits to a "tube " you may still be able to chuck the tube and use a fixed steady on the other end, still a lot of tool overhang though.

Jason


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## SignalFailure (Dec 15, 2009)

Putputman:

Thank you, that's nice and clear. I've read about that type of bar with a screw to adjust cutter position along with a locking grubscrew but never seen one before. 

Is there any disadvantage with using a (easier to make!) fixed point bar and using the cross-slide to alter the depth of cut instead? (I suspect the answer will be that the cross-slide may not move perpendicularly to the bore but I'll ask anyway!)


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## tel (Dec 15, 2009)

No way that's gonna work Paul, as soon as you move the cross slide the tool will start taking material from one side of the hole and leaving the other alone. Totally useless unless you are trying to machine some egg-shapes.


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## scoop (Dec 15, 2009)

when I measure awkward bores on a lathe I use a lever type DTI in a hight stand and stand it on the cross slide and find the highest part of the bore and zero the DTI then transfer to a surface plate and measure the hight with a tower gauge.Then do the same with the lowest part of the bore and measure that then subtract the small size from the big size to get the bore diameter.The boring bar may make the job a bit trickier but possible.

good luck Steve C


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## putputman (Dec 15, 2009)

Paul, I think Tel answered your question very well.

To add a little more information on my set up. The first thing I did was to remove the compound from the crosslide. I then established a dimension from the crosslide to the center of the lathe. Very important. I recorded that dimesion for any future set ups.

Next I determine the distance from the base of the engine to the cylinder bore. The distance from the crosslide to lathe center minus the distance from the engine base to cylinder bore is the thickness of the mounting plate for this set up. This will establish the vertical height and vary from engine to engine.

The horizontal location was established by locating and doing a roughing cut on the mill. Then once it is set up in the lathe, I mounted a TDI in the chuck & zeroed in the location with the crosslide. That is when I set the crosslide indicator to zero also.

This sounds like a lot of work but once you do it you will find it doesn't take that long. You will also find that holding the long boring bar in a chuck with a live center on the outboard end will provide a very rigid set up and a very smooth cut. You should not have any chatter in the bore.


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## SignalFailure (Dec 15, 2009)

Hmmm, this is rather more complicated and takes more equipment than I have at my disposal. It'll have to wait until way after Christmas 

Thanks everyone for the help


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