Boring 6" (150mm) deep .

[stragenmitsuko]

So I need to bore a 1-3/4 by 2.5" ( 64*45mm) aluminium block with a length of 6" ( 150mm) .
Bore needs to be parallel to at least one surface , altough that could be milled later on .
Bore diam would be 1.40" ( 36mm ) .
As this will be a cilinder for a gas engine , some degree of acuracy is required , altough a liner will be pressed in afterwards .

Option A : hold it in a 4 jaw , that would leave abt 4" sticking out .
I can hold it in the 4 jaw , but it won't pass the bore in the chuck .
Then use a heavy boring bar and machine to size .

Option B : clamp it to the mill table , and use the mill in horizontal setup
in combination with a boring head and again a large boring bar .

Option C would be to line bore it , wich would be the best option by far .
But helas , none of my machines will allow this .


Thoughts :

In the lathe the bore can be finished to closer tolerances , and most likely better finish . But parallelism
to the surfaces can't be guaranteed . I know I can indicate it but still . It'll be only an 1-1/4 (30mm) in the jaws .
If the block is a bit oversized maybe it can be milled afterwards to produce the surfaces parallel to the bore .
On the mill however , clamped to the table the bore will be parallel to the table , but with a boring head I'll be lucky to
obtain the correct dimension and avoid boring a taper .

So none of these options really pleases me , but I need to make a decision on this .


Normally one would use cast iron for a cilinder . Wich I don't have , and can't obtain .
So I thought I'de use an ali body and press in a sleeve .
Can I use steel for the sleeve ? Same problem , don't have any cast available .
Thougt maybe I'de use seamless black pipe to make the sleeve .
The piston is aluminium with cast iron rings .
Sleeve offcourse will be honed or lapped once the cilinder is finished .
It will also require carefull machining to obtain a decent press fit , but that
is possible with the machines I have .
The black pipe will pass the chuck body to bore the inside , then it can be put on a mandrel to machine the outside .

Thx

Pat

 

[WOB]

Option A. Black pipe does not machine nicely. Make the sleeve out of 12L14. Finish bore before inserting in alum. block. No need for a press fit. Just make it easy push fit and coat with Loctite 638 or similar. That way no distortion of bore on insertion.


WOB

 

[fcheslop]

4 jaw and a fixed steady

 

[goldstar31]

Mount it on the saddle and use an inline boring bar- between centres

I used TWO to bore the castings for the Quorn tool and cutter grinder- and these not only had to be perfectly parallel but parallel for TWO PGMS 1" Dia round bars- 13" long then a vertical column- with an 1.25" round with a 1" TPI thread!

The boring bars were done to George Thomas's book. Model Engineers' Workshop Manual.
See the correspondence about the book now.

Assuming the lathe bed is square, and even if the tailstock is 'out' the bore will parallel.
Mathematically, the bore MUST be parallel but what sort of metal- is anyone's guess!

Norman

 

[stragenmitsuko]

Thx for all the replies .

@WOB
I don't have any 12L14 . Wel maybe I do , but I don't know what I have .
I have loaded a trailer full of bar stock once , all from a company that went broke .
But sadly it is all unknown material . I could offcourse try something that machines nicely
and hope for the best .
Will locktite 638 or similar hold when the cilinder heats up ? I agree it's tempting
to avoid any distortion .

@fcheslop
4jaw and a fixed steady . I guess a square part won't run true in a 4 jaw .
But then again I could turn a small section round to use the steady .
Good idea . I need to give this some thought . It would solve the long stickout problem .

@goldstar31 .
Yes line boring would be the way to go .
But my lathe has no t slots on the carriage or cross slide or compound .
As I said , line boring is not possible with the equipement I have.
Otherwise I wouldn't give it a second thought .

 

[stragenmitsuko]

btw what would happen if I don't sleeve and just run it in the aluminium cilinder .
Won't last long , but it's not supposed to run every day either .
The question is how long would it last .
That is offcourse assuming it will ever run .

 

[TonyM]

Do you have spare material on the length. If so 4jaw, Centre end and turn back enough to use a fixed steady. Bore as required. .
I personally would have no concern with boring aluminium just using the 4jaw. Just take smaller cuts.

 

[goldstar31]

@goldstar31 .
Yes line boring would be the way to go .
But my lathe has no t slots on the carriage or cross slide or compound .
As I said , line boring is not possible with the equipement I have.
Otherwise I wouldn't give it a second thought .

Probability that a Bell chuck or a cat's paw chuck would be OK.

The late (Sir)John StevensonMBE ( Motor bike engineer) teased each other years ago here.

Seemingly, our words fell on deaf ears

Sad isn't it?


Norman

 

[stragenmitsuko]

a bell chuck in the steady rest ...... that ought to work .
good thinking !

 

[SmithDoor]

Typically I would use a mill.
The other way is remove the compound from the lathe and make jig to hold the part on the carriage. Now you use the cross slide to space the holes.

Dave

 

[Ghosty]

These are some that I have done, all on lathe, not a problem. Cast iron cylinder liner, brass cylinder.
Question, What is the stroke, and the piston height?, a 6" bore on a 1-3/4" bore, you will have problems with clearence of the con-rod

 

[stragenmitsuko]

It's like an opposed piston engine . That is why it's such a deep bore .

Nice engine with the brass cilinders .