Boring a Deep Hole

[doubleboost]

(07-17-2013, 04:38 PM)EdK Wrote:

(07-17-2013, 02:54 PM)doubleboost Wrote: You could always mount the job on the lathe cross slide and put the boring bar between centres
This is how I bore my engine cylinders
Use a big drill from the headstock first

John

Hi John,

I thought of that also. Isn't that called line boring?

I wondered how well it would work on a 1.5" hole. I thought that size hole might be too small for line boring, but I don't know.

Ed

You would use a one inch bar
(not much flex on that)
Depends on your cross slide
Mine has tee slots
John

[Hopefuldave]

Ed, John's hit the nail on the head, and.beat me to it

Between-centres bar would.do a good job, if you can clamp the work to the carriage, and guarantees a cylindrical, uniform bore (cos the bar always flexes the same throughout the bore, same load at same point). Not expensive to tool up, either, compared to a boring head....

[EdK]

John,

Could you post a closeup of the cutting bit in the boring bar that's between centers? How do you advance the cutter to enlarge the hole?

Thanks,
Ed

[stevec]

(07-19-2013, 02:45 AM)Hopefuldave Wrote: (cos the bar always flexes the same throughout the bore, same load at same point).

Dave, could you elucidate as to why a "one end supported" boring bar, as in a boring head, would flex more (or less) at entry of the bore than at the end/exit?

[doubleboost]

Pictures of the cutter in my boring bar
The bar is 24 mill bright steel bar
The cutter is a 1/4 inch broken centre drill




As you can see it is locked in place with 2 bolts (flat ground on to cutter)
The depth of cut is measured with a clock guage directly on to the cutter
A block and small bolt are held on to the back of the bar and used to push the cutter through

John

[EdK]

Thanks Hohn!

Ed

[doubleboost]

(07-19-2013, 03:42 PM)EdK Wrote: Thanks Hohn!

Ed

John

[EdK]

Well, I'm glad I procrastinated in getting a 3" boring head. I used the Enco 25% off and ordered it yesterday. Even with the 25% off I had to go with the import model but it's better than nothing.

Ed

[wrustle]

Now that I kinda understand your application, how are you going to determine the hole size, taper and straightness?

While pressing in a sleeve that size, that long with an interference fit in aluminum is going to be a challenge in itself given the fact you most likely will not have the greatest surface finish nor a true round thru bore (I imagine peaks and valleys like a vac hose....exaggerated example, but gives you an image) that will not be tapered.

Using the quill on your knee mill will get you the result you desire as far as a 1.5" dia. thru the material, but as far as taper and surface finish go, it's going to be difficult at best, UNLESS you have a very tight machine, that is trammed in dead square.

Your best bet is following Johns suggest of boring in the lathe using the cross slide to hold your part.

When making your boring bar be sure to use a fine pitch set screw to push the bit out of the bar, that way you will have better control of your size as you just need to know how many thousands per inch each revolution of the screw is, and you can dial it in pretty damn good in that manner.

That 3" boring head sticking out of your quill with a 5 or 6" boring bar sticking out of that (whether it be carbide or not) is not going to be doing you any favors in achieving a decent surface finish, which will translate into a tapered diameter that will be all over the place in size as you measure it thru.

When you do get your hole bored, and your sleeve made, (not knowing the wall thickness here but this will help nonetheless) place that sleeve in your freezer for the day. Keep the mating piece room temp. Do not heat it up! When ready, pull out the sleeve (using gloves to hold....no warm hands) and get it into your bore ASAP and pressed in (again depending on the wall thickness determines the shrinkage) and you should be good to go!

Good luck!
Russ

[EdK]

Yikes! Now I don't know which way to go with this. Decisions, decisions.

The wall thickness of the sleeve will be about 1/4" thick. It only needs to be a light press fit since I'll be pinning the sleeve to the aluminum block. The ID of the sleeve needs to be fairly accurate since it's going to accept a MT-2 sleeve that will need to move in and out via a screw on the end. This project is a ways down the road so I have some time to think about it.

Thanks for all of the suggestions and help everyone.

Ed