[artin51]

Hello everyone,
Just want to get people's opinion on using a boring head to get a hole to size. I'm looking into pulling the trigger on a boring head kit from iscar and would like to know of any issues people have had. Obviously the machine spindle has to be in good condition and the work rigid. Can i expect to get holes with to within +/-.00025" on the diameter? Assuming normal usage conditions?

thx

[laka]

Depending on the number of holes you need to bore, repeatability of the desired size may be a problem. If you have spindle air-blow during tool change this will help a lot. I've had boring heads cut large/small from having dirt/small chips on the taper and thowing it out a little.

On our machine with spindle air-blow we run our sandvik boring heads all day and they will stay within +/- 0.0005 for sure. Make sure you rough the hole out with an endmill before boring, leaving the same amount of stock on every hole so you dont have to worry about deflection too much. On holes up to 1" we usually leave 0.002 to 0.004" on diameter to bore. Over 1" maybe 0.005" to 0.008", we have good luck using wiper inserts to get good finishes.

Good luck

[DareBee]

I think .00025 is pushing it a bit for a boring head. It is possible but not so realistic.
Half thou would be usual expected tolerance.
If you wish to get fussier than that you really should go to jig grinding.

[Geof]

I think .00025 is pushing it a bit for a boring head. It is possible but not so realistic.
Half thou would be usual expected tolerance.
If you wish to get fussier than that you really should go to jig grinding.

I thought +/-0.00025" is half a thou.

[KyleH2]

I thought +/-0.00025" is half a thou.

No that would be a quarter thou.
.001/2 = .0005
.001/4 = .00025

Anyone know where I can get a 4" boring head? Also it needs to go on an MT2 taper 1/2HP Bridgeport, is that too small for that big of a boring head? I need to bore a 3.5" hole.

[Geof]

No that would be a quarter thou.
.001/2 = .0005
.001/4 = .00025

.

If I have a nominal size that is permitted to vary +0.00025 and -0.00025 the difference between the largest permissible size and the smallest permissible size is 0.00025 + 0.00025 which is 0.0005.

[DareBee]

You know what I mean Geof.

Yes Kyle that is too big.
Also, if you intend to do milling with a MT taper please wear a baseball glove and be prepared to use it at any given moment.

[hoidahl]

We use the iscar ITS bore heads. They are very accurate and we have held +/- .00025 but we hand loaded the tool each time and had small quantity of parts.

[KyleH2]

You know what I mean Geof.

Yes Kyle that is too big.
Also, if you intend to do milling with a MT taper please wear a baseball glove and be prepared to use it at any given moment.

I am not positive its an MT2 as it is not my machine nor have I spent any time playing with it. Its a little 1/2 HP baby Bridgeport, I think a BRM. If it is they came in Morse 2, B&S #7 and Standard B-3(never even heard of this one :P). I am just assuming (yes I know what happens) its MT2. That would be convenient because you can actually get boring heads and collet chucks for MT2 spindles easily and cheaply. Right now all he has are collets.

[artin51]

Thanks for the reply guys. I'll go ahead and purchase the kit. For your information the iscar kit that does .24 to 1.13in diameters with the CAT40 adaptor was quoted to me around 2000$. At the moment we send the parts to get honed, so i'm trying to bring the process in house.

[juergenwt]

+/- 0.00025 not a chance. Save your money. Juergenwt.

[Palerider]

Save the boring for last, dial it in, and don't remove the holder between parts.
If tool wear isn't a big issue or lack of material homogenosity it should be right there every time.

[KTD1]

We use the URMA Boring System. We hold +/-.0002" bore sizes on a regular basis. They are not cheap but we like them. Visit www.commandtool.com for more information.

[Cruiser]

I have in the past done many thousands of holes with tollerances of total .0006" in a large cnc lathe. The machine, bore gauge, the all important bore gauge standard ! (of which we usually made for the job) ALL were susseptable to thermal variations even by holding in the hand a bit too long, and during winter the machine was very kinky and during summer it all was worse ! Every hole was considered to be custom made and we had to back off and sneek up on each hole in process. The guys in the mill department had the same issues. If your part is cheap enough that you don't mind throwing some of them away then just shoot for it and adjust. If they are expensive then don't trust anything till it clears the final inspection process ! If you have climate control through the whole process then your job will be lots easier, our shop had some enormous doors that were always going up and down at the wrong time ! Good luck to you !

[cam1]

Hi:
1 question: What is the reason for the tight tolerance on the bore? For a dowel pin?
Reaming is an option, so is ball sizing.


regards

[artin51]

The current part is an aerospace hinge support that gets bushings pressed-in. It won't be high production. 15-20 parts at a time. I hadn't thought about ball sizing, having never used it personally. Might be an option. Anyone used this method successfully?

thx

[cam1]

Hi:

Try this link

http://www.precisionballs.com/Ball_Sizing.htm

http://www.precisionballs.com/

regards

[artin51]

Hi cam,
thx for the links. I'm just curious if it's plain precision, hardened balls that can be used. I think it's worth a shot seeing as how the balls are fairly cheap. Will definetly look into it.

thx again

[cam1]

Cheers

[cam1]

If it's 6061 T6, I'd go with unhardened run of the mill balls.
Keep us posted of your success/trials, as it will build the knowledge base.

regards