Bore Gauge

[Griffin]

Bore gauge

I’m building a PMR #5 bottle engine at present & while turning the brass piston noticed it was 5 thou bigger one end than the other, this prompted me to check the cylinder bore and behold that to was cone shaped, so, pulled lathe apart, bashed it with a hammer a few times, centred spindle thanks to Rollies dad, re-bored cylinder and all seems ok, but, I was wondering what you guy’s use to measure the inside bore of say ½” to 1” Dia holes? My cylinder's stuck in the chuck at the moment not knowing if its straight or not and wondering if I’m missing the obvious? :wall:

Mark

 

[Tin Falcon]

I was taught in tech school to use t gauges to measure bores .

the simplest method but a little time consuming.

You can get bore indicators. They take time to set up but a direct measurement .
inside mics are nice but hard to check for taper. as you can only check one end without taking the part out of the lathe.
bore mics IMHO out of the price range of most hobbyists.
Tin

 

[aonemarine]

Shars on eBay has dial bore gauges pretty cheap. I have one from them and it works well. You will also need a micrometer to set it...

 

[Forestgnome]

Shars on eBay has dial bore gauges pretty cheap. I have one from them and it works well. You will also need a micrometer to set it...

Just be aware that many dial bore gages are three-point measurement systems. You can't calibrate those with a micrometer, you need a setting ring. Setting rings get expensive real fast. You can use a three-point bore gage for comparison though. I have one I use for determining taper and ovality in cylinders, no setting required, all relative measurement.

 

[Lakc]

I have a set of ball gauges for up to 5/8" I think, then its T gauges until about 2" where I have a starret bore gauge. The Starret is kinda a T gauge with a dial indicator and three point centering, you can lock its measuring arms and read it like a T gauge if you want. Shame it isnt any smaller. I have enough stuff to cobble together an air gauging system but I am not building any rifle barrels.

 

[Tin Falcon]

when I worked in the grinding shop We used an air comparator dead on easy measurements to the 0.0001 but you need to set them to a ring Gage.
And you need to get close to use them as they have a limited range . meant mostly for measuring the last bit as in grinding or lapping.
a ring gauge is not hard to make since they do not need to be long like a bore.


But the old horse cat chicken egg delema. you need to machine an accurate bore . You are struggling to get a good measurement for known acuracy . so how do you make a Gage to check accuracy.

I actually have a federal air comparator I bought on e bay . I need to set it up and make tooling for it. The editor of Home shop machinist asked me to write up and article. AAH things to do.
Tin

 

[Tin Falcon]

Tapers are not uncommon make sure you use the biggest boring bar you have keep the tool sharp and take spring cuts.

Tin

 

[gus]

Just be aware that many dial bore gages are three-point measurement systems. You can't calibrate those with a micrometer, you need a setting ring. Setting rings get expensive real fast. You can use a three-point bore gage for comparison though. I have one I use for determining taper and ovality in cylinders, no setting required, all relative measurement.

The 1" Mitutoyo Bore Mics came with a Bore Gage. Same mike was very expensive.

 

[gus]

when I worked in the grinding shop We used an air comparator dead on easy measurements to the 0.0001 but you need to set them to a ring Gage.
And you need to get close to use them as they have a limited range . meant mostly for measuring the last bit as in grinding or lapping.
a ring gauge is not hard to make since they do not need to be long like a bore.


But the old horse cat chicken egg delema. you need to machine an accurate bore . You are struggling to get a good measurement for known acuracy . so how do you make a Gage to check accuracy.

I actually have a federal air comparator I bought on e bay . I need to set it up and make tooling for it. The editor of Home shop machinist asked me to write up and article. AAH things to do.
Tin

Hi Tin,

My Campbellsville,Ky QA friend went all the way to NW India to set up Air Gaging Stations for Con-Rod vendors. Nobody there ever heard of Air Gaging.
This was wayback in 1999. Today they swear by it.
NW India is quite an interesting place to visit. But you cannot drink their local
water. My friend survived on Bottled Mineral water for 2 years.

 

[Griffin]

OK, many thanks guy’s for taking the time to reply, I justbought a set of “T” gauges from Chronos, the price more reflects the use theywill get, just have to learn how to use em’ now, but I have the time to learn, Iactually tried using a boring head in the mill but that cut a 12 thou taper soI then I tried using the lathe with the same taper effect.

Poor casting is getting a little thin now, it started outneeding 0.625in bore and a last measure was 0.648in, long straight holes don’tseem to be my thing here. At the moment I’m trying to fathom a way to cut thegrove for the eccentric to run in, so probably be another question about thatwhen I get round to it.



Mark

 

[cncjunior]

Hi Griffin,

I have a few suggestions that might solve the taper bore problem. I have learned about these the hard way myself. The first would be to make sure the tool height is on the center of the hole. The other would be to make sure there is enough relief under the cutter to clear the bore. Some of the boring bar sets that come in a wood box or plastic container don't have enough side relief on them to start. What I found is that as the b. bar goes in the bore during a cut the tool would be forced up and cause the bore size to have a taper.

Daniel

 

[Hopefuldave]

One way to get a decently cylindrical bore is with a boring bar between centres - a bit old-school, and means you need a way to set the work on the cross-slide, but any flex in the bar is constant. For a bore that small you'd be using a 1/2" bar, so there would be flex! You could minimise it by using the shortest possible bar.

Another possibility would be a D-reamer made for the job, silver steel, hardened and tempered, works for ally, brass, bronze, cast iron and unhardened steels.

Just my ha'pennorth,
Dave H. (the other one)

 

[Swifty]

Mark, strange that you get the same taper in both your mill and lathe. You can get a tapered bore in a lathe if the headstock is out of alignment, but using a boring head in a milling machine should give you a parallel bore, unless you are getting too much spring in the boring bar. Is there a hard spot in the casting you are trying to bore, could be knocking off the tip of your boring bar.

When using telescopic gauges, it is important to give the gauge a slight bit of preload, then nip the lock up and tilt it in the bore only once. Don't be tempted to tilt the gauge back again, once you have tilted it through once, withdraw the gauge and check the size with a micrometer. Check the bore a couple of times to make sure that it is consistent.

Paul.

 

[Swifty]

This video explains how to use telescopic gauges.
[ame]http://m.youtube.com/watch?v=SmXfGan_NXQ&feature=related[/ame]

Paul.

 

[Griffin]

Daniel, thanks for that, but in this case its not the boring tool, the finish is like glass, just tapered. Paul thanks for the video, its the first time I've seen on being used and was very helpful, Dave H, I tried making a tool for the mill with silver steel as was sugested by Tin, believe it or not about a 5/16in tapered reamer I bought, but the results were very poor, thats why I tried the lathe.
Mark