I have seen several posts where the poster indicated that they had measured a bore and found, for example, that it tapered .0002 in an inch. While I know this level of precision is possible, I'm curious what tools and set ups are used in a typical home shop that allow this level of measurement with any confidence. Anyone have any tips to share??
Measuring bores
- Thread starter Ed T
- Start date
Help Support Home Model Engine Machinist Forum:
The dial bore gauge is within most hobbyists budget once you become serious about measuring this sort of thing. Second hand they can be had at very reasonable prices.
http://www.mitutoyo.com/TerminalMerchandisingGroup.aspx?group=1519
http://www.mitutoyo.com/TerminalMerchandisingGroup.aspx?group=1519
- Joined
- Jan 19, 2010
- Messages
- 1,193
- Reaction score
- 41
Ed, when I am measuring a bore I use a Dial Bore Gauge. They are actually quite affordable on e-bay.
A tip for purchasing one (If you so decide) is to get the dial bore gauge with a .001" indicator,(this will save you money) then purchase a dial indicator that reads in tenths (.0001") which is also quite affordable on e-bay.
These dial bore gauges accept 3/8 shank indicators, which is virtually every one. So choose a dial indicator with a .small measuring range, (I chose .05" travel) all you need is about .02 travel for the bore gauge.
Hope this helps.
A tip for purchasing one (If you so decide) is to get the dial bore gauge with a .001" indicator,(this will save you money) then purchase a dial indicator that reads in tenths (.0001") which is also quite affordable on e-bay.
These dial bore gauges accept 3/8 shank indicators, which is virtually every one. So choose a dial indicator with a .small measuring range, (I chose .05" travel) all you need is about .02 travel for the bore gauge.
Hope this helps.
When boring, use the largest boring bar you can get up the hole, and make sure the tool is razor sharp and exactly on centre. If it is a thru bore, try to get a small radius on the tool nose, it will give a better surface finish.
If possible, carry out all cutting under power, both in and out, hand feeding will contribute to inaccuracy in the bore surface, and make sure all your gibs are nice and snug, but not tight. You will have enough trouble with tool flex without the machine contributing to the problem.
For your final pass, which should only be a couple of thou at most, go in and out at the same setting at least half a dozen times, maybe a lot more. You might find it is still creating 'fairy hair' for a long time, as it gradually skims off material left behind from the previous cuts where the tool flexed and left you with a tapered bore. Just keep cutting until you get no more fairy hair or dust being produced at all.
For small bores, you can't get much up the bore to measure with any accuracy to see if it is tapered or not. For larger ones, you can use an internal bore mic or a clock bore gauge, but they all come at a price. I have ones going from 1mm upwards, and you don't want to know how much they cost to buy new. But the larger sizes do come at very reasonable prices, around 30 UK pounds for each measuring range.
Don't even think about digiverns for measuring with any accuracy, you are lucky if you can get within a couple of thou, and because of the flats on the edge of the internal nibs, the accuracy is even worse.
Once you have removed the part with the bore from the chuck, never consider putting it back in to remachine if the bore is slightly out. No matter how close you get the settings to perfect, you will never be able to pick up the original bore exactly. Once out of the chuck, the only way to straighten things up is to lap exactly to size.
If possible, carry out all cutting under power, both in and out, hand feeding will contribute to inaccuracy in the bore surface, and make sure all your gibs are nice and snug, but not tight. You will have enough trouble with tool flex without the machine contributing to the problem.
For your final pass, which should only be a couple of thou at most, go in and out at the same setting at least half a dozen times, maybe a lot more. You might find it is still creating 'fairy hair' for a long time, as it gradually skims off material left behind from the previous cuts where the tool flexed and left you with a tapered bore. Just keep cutting until you get no more fairy hair or dust being produced at all.
For small bores, you can't get much up the bore to measure with any accuracy to see if it is tapered or not. For larger ones, you can use an internal bore mic or a clock bore gauge, but they all come at a price. I have ones going from 1mm upwards, and you don't want to know how much they cost to buy new. But the larger sizes do come at very reasonable prices, around 30 UK pounds for each measuring range.
Don't even think about digiverns for measuring with any accuracy, you are lucky if you can get within a couple of thou, and because of the flats on the edge of the internal nibs, the accuracy is even worse.
Once you have removed the part with the bore from the chuck, never consider putting it back in to remachine if the bore is slightly out. No matter how close you get the settings to perfect, you will never be able to pick up the original bore exactly. Once out of the chuck, the only way to straighten things up is to lap exactly to size.
Tin Falcon
Well-Known Member
- Joined
- Jul 9, 2007
- Messages
- 7,207
- Reaction score
- 787
I learned to measure with small hole gauges and t gauges of course you take the actual measurement with a Micrometer.
I may add dial bore Gage at some point . Bore mics are nice but limited in range and expensive.
I have a pneumatic comparator but need to make gauges for it.
Tin
I may add dial bore Gage at some point . Bore mics are nice but limited in range and expensive.
I have a pneumatic comparator but need to make gauges for it.
Tin
doc1955
Gone
- Joined
- Aug 26, 2009
- Messages
- 1,261
- Reaction score
- 164
I seem to remember reading about some home shop made bore dials made with a dial indicator.
I remember at the time I thought hey these would be a nice addition then I apparently seen some thing else that caught my eye and forgot all about it.
I personally use snap gauges in my home shop but would only trust them to .0005. I have seen some that claim that they can read them even closer but I personally am not able to trust them beyond the half thousand mark.
At work I used a dial bore or a pneumatic and a standard and also have used a hone gauge.
I remember at the time I thought hey these would be a nice addition then I apparently seen some thing else that caught my eye and forgot all about it.
I personally use snap gauges in my home shop but would only trust them to .0005. I have seen some that claim that they can read them even closer but I personally am not able to trust them beyond the half thousand mark.
At work I used a dial bore or a pneumatic and a standard and also have used a hone gauge.
rake60
Well-Known Member
- Joined
- Jul 8, 2007
- Messages
- 4,756
- Reaction score
- 124
I'm a bit "Old School" when it come to measuring small bores.
I still use telescopic gauges.
They work like this:
[ame]http://www.youtube.com/watch?v=LXTOlSnIo4k[/ame]
You do need to develop a feel for using them but if used properly they are
as accurate as any "new" method.
Rick
I still use telescopic gauges.
They work like this:
[ame]http://www.youtube.com/watch?v=LXTOlSnIo4k[/ame]
You do need to develop a feel for using them but if used properly they are
as accurate as any "new" method.
Rick
d-m
Well-Known Member
- Joined
- Mar 20, 2008
- Messages
- 211
- Reaction score
- 5
I also use telescopic gauges it takes a good feel to get it right.The trick I found for using them is check your bore several times. When I started using them I would check till I was sure I had several readings the same, now I just check twice unless they are not the same. Hope I did not confuse any one.
Dave
Dave
YUP I have a set of bore gauges like that Rick.
They can be sensitive/tricky to use the first time, but you get the hang of it.
A way to practice with them is to measure a lot when the bore is still undersize, and then see how small you can open the bore repeatably.
Say you want .875" ultimately. Start measuring when the bore is .740" and slowly open the diameter up with a boring bar to .745"..then .748 and then .749....try for .7495", then if your feeling daring .7498.
Now if your really adventurous, and "gotta know". before the above excercise, Make up a plug guage that is exactly .749 diameter for the first 1/8" length, and then exactly .7500 diameter for the next 1/8" length.
With this plug guage, you can cross check your bore guage measurements, bracketing them. At about .7492 the plug guage will go in 1/8" and stop. Then you know your between ,749 and .750.
It all doesn't matter at this point as you still need to take another .125 out of the bore of your work piece, but you will have developed the "feel" required to use the guage "in anger" when you start sneaking up on .874....8745...ect.
This is all a great excercise and can be fun to challenge yourself. Additionally, you learn something about how your lathe and tools react under these conditions. Is your tool cutting right? Are your carriage gibs loose? Are you getting the finish you want?...ect.
Dave
They can be sensitive/tricky to use the first time, but you get the hang of it.
A way to practice with them is to measure a lot when the bore is still undersize, and then see how small you can open the bore repeatably.
Say you want .875" ultimately. Start measuring when the bore is .740" and slowly open the diameter up with a boring bar to .745"..then .748 and then .749....try for .7495", then if your feeling daring .7498.
Now if your really adventurous, and "gotta know". before the above excercise, Make up a plug guage that is exactly .749 diameter for the first 1/8" length, and then exactly .7500 diameter for the next 1/8" length.
With this plug guage, you can cross check your bore guage measurements, bracketing them. At about .7492 the plug guage will go in 1/8" and stop. Then you know your between ,749 and .750.
It all doesn't matter at this point as you still need to take another .125 out of the bore of your work piece, but you will have developed the "feel" required to use the guage "in anger" when you start sneaking up on .874....8745...ect.
This is all a great excercise and can be fun to challenge yourself. Additionally, you learn something about how your lathe and tools react under these conditions. Is your tool cutting right? Are your carriage gibs loose? Are you getting the finish you want?...ect.
Dave
doc1955
Gone
- Joined
- Aug 26, 2009
- Messages
- 1,261
- Reaction score
- 164
rake60 said:
These are what I was referring to around our shop they had been called snap gauges and I agree you really do have to develop a feel for them. These are what I've been using for 37 years now and have (as far as I can remember) never failed me.
I think Ed T is after measuring bores a lot finer than the 'telescope' or 'snap gauges' can give.
The problem with them is that they are not in real time, which clock gauges are.
With the telescope type, you are taking a measurement, which is purely by feel, then remeasuring with a mic, again usually by feel, and that is where the inaccuracies arise. It used to be the old internal calipers and mic before telescope bore gauges came along and sold to the masses, and again, they were only as accurate as someone could 'feel'. Two people could get two different results, both usually within drawing tolerances, but different all the same.
Clock bore gauges give a real time reading while actually moving around inside the bore.
I am not saying that the telescoping type are no good, but because of the transfer between two measures, can, and do, give varying degrees of accuracy, and certainly not up to Ed T's expectations.
Clock bore gauges and three point bore mics do give that required accuracy while still in the bore.
So this really is a case of, if you want the fine accuracy, you have to reach a little deeper into your pocket.
The problem with them is that they are not in real time, which clock gauges are.
With the telescope type, you are taking a measurement, which is purely by feel, then remeasuring with a mic, again usually by feel, and that is where the inaccuracies arise. It used to be the old internal calipers and mic before telescope bore gauges came along and sold to the masses, and again, they were only as accurate as someone could 'feel'. Two people could get two different results, both usually within drawing tolerances, but different all the same.
Clock bore gauges give a real time reading while actually moving around inside the bore.
I am not saying that the telescoping type are no good, but because of the transfer between two measures, can, and do, give varying degrees of accuracy, and certainly not up to Ed T's expectations.
Clock bore gauges and three point bore mics do give that required accuracy while still in the bore.
So this really is a case of, if you want the fine accuracy, you have to reach a little deeper into your pocket.
All the above is sound advice and since I don't own a set of telescopic gauges (here I agree with Bogs they are subject to the vargaries of "feel") so I go with Tel's plug on a stick method.
As Bogs stated verniers are useless unless you calibrate them on a known testpiece of similar diameter first - and even then you might need a pinch of salt + 1 digit.
Can't beat a bore micrometer.
But since we are modeling and not into production tollerancing why not machine the bore and then machine the "plug" part to a tight fit, mic it and add the required clearance.
Ken
As Bogs stated verniers are useless unless you calibrate them on a known testpiece of similar diameter first - and even then you might need a pinch of salt + 1 digit.
Can't beat a bore micrometer.
But since we are modeling and not into production tollerancing why not machine the bore and then machine the "plug" part to a tight fit, mic it and add the required clearance.
Ken
A local used machinery dealer once showed me a home-made tool he got in a job lot, I'll try to describe it. It was like a short squat vernier caliper with radiused inside jaws. Looked to work from about 15mm bore to about 40mm. You put the tool jaws in the bore then adjusted them outwards with a thumbscrew until they contacted the sides then removed them and measured across with a micrometer. I guess this tool needed a lot of 'feel' to get accustomed to aswell but it was really nicely made an smooth.
Hi Guys,
Dial bore gauges (DBG)are great for measuring to see if a bore is tapered, ie working as a comparator (which is what they are), but they are a grade 1A pain if you want to know the real diameter of the bore. "Ring gauges" I hear you say, well great idea but how do you measure one of those, except with a dial bore gauge, Catch 22 anyone?
Have any of you Guys tried to get a consistent reading from a DBG with a Micrometer, not easy to do without more than the usual compliment of hands. :idea: Perhaps a stand is called for to hold the gauge while measuring is done, oh no, yet another item for the Tuit list.
I think I have discovered "perpetual motion" it's a HMEM's Tuit list, well there is no end in sight of mine.
Ned
Dial bore gauges (DBG)are great for measuring to see if a bore is tapered, ie working as a comparator (which is what they are), but they are a grade 1A pain if you want to know the real diameter of the bore. "Ring gauges" I hear you say, well great idea but how do you measure one of those, except with a dial bore gauge, Catch 22 anyone?
Have any of you Guys tried to get a consistent reading from a DBG with a Micrometer, not easy to do without more than the usual compliment of hands. :idea: Perhaps a stand is called for to hold the gauge while measuring is done, oh no, yet another item for the Tuit list.
I think I have discovered "perpetual motion" it's a HMEM's Tuit list, well there is no end in sight of mine.
Ned
Just recently I made a part, actually it's still in the chuck while I determine what to do next, probably lapping. I have a 5.5" deep thru bore 1.5" ID. I ended up with about .002" of taper. I used an elcheapo import 3/4" boring bar sticking out past the holder just a hair more than needed to clear the depth. I'm cutting aluminum, with an aluminum insert so cutting went well. I went from 1" ID tube to almost 1.5" in two passes. I knew I was going to have some taper in the ID even though I managed to set the bed to cut without one on the OD over the same length. Had I thought about this a little further in advance I would have readjusted the bed to get a good ID. Now there is very little room left for cleaning up, but I might still go that route. With almost 6" of bar hanging out from the tool post the carriage is that much further down the bed and running on a portion that wasn't used much. Being a Clausing machine I wasn't expecting much wear of the ways, but there is some wear as the carriage is tighter out there. Is you are trying to measure a bore in aluminum lubricate your snap gage or bore gage, the aluminum was very sticky and made it difficult to measure anything without.
BTW, I have a set of B&S snap gages I can't get to work well at all. It seems when I tighten the thimble before pulling it from the bore it retracts the points a touch and is sloppy in the bore. I did the register for a chuck backplate with a borrowed snap gage before I had mine and things went fine and was able to seemingly get withing a few tenths on feel.
I am able to set my bore gages with a mic. It takes some effort.
BTW, I have a set of B&S snap gages I can't get to work well at all. It seems when I tighten the thimble before pulling it from the bore it retracts the points a touch and is sloppy in the bore. I did the register for a chuck backplate with a borrowed snap gage before I had mine and things went fine and was able to seemingly get withing a few tenths on feel.
I am able to set my bore gages with a mic. It takes some effort.
Lakc
Well-Known Member
For smaller bores then the telescoping or snap gauges can measure, I use a set of ball gauges. Same variances due to feel, but they work well enough that I have not needed to get smaller 3 point dial gauges like the big one in the pic. Bogs is correct, 3 point dial gauges, and a matching ring gauge, are the best way to do it, but I dont feel like I am suffering using what I have.
The biggest hassle measuring bores, at least on the lathe, is winding the carriage far enough out of the way to use any of these tools. :-\
doc1955
Gone
- Joined
- Aug 26, 2009
- Messages
- 1,261
- Reaction score
- 164
In my opinion yes dial bore gauges are the way to go if you can justify the funds for the added accuracy but along with the dial bore gauge you almost need a set of gauge blocks to set them up properly. If they are not set up correctly they are no more accurate than snap gauges.
With care, spring internal calipers can get you to within 0.001 ins but don't work for small bores. I got this set from Ebay, old but still functional range 1/8 - 1/2 ins with 0.0001 resolution but still needs some care.
http://s757.photobucket.com/albums/xx213/dvbydt/Engineering/?action=view¤t=JohnBull.jpg
When you get to tenths, the only real answer is honing to get straight, round and size. Google Sunnen for information on both internal and external hones. A bit expensive for the home workshop so count yourself lucky if you find a bargin and can afford the hones.
Ian
http://s757.photobucket.com/albums/xx213/dvbydt/Engineering/?action=view¤t=JohnBull.jpg
When you get to tenths, the only real answer is honing to get straight, round and size. Google Sunnen for information on both internal and external hones. A bit expensive for the home workshop so count yourself lucky if you find a bargin and can afford the hones.
Ian
