turning cast iron coupling

[welder]

i have to machine a cast iron love joy coupling i have to bore the internal diameter to 1.5 inch i can do it on the lathes at school but i know cast reactes differently when machined when compared to steel can a bore it out with a boring bar if so how should i go about doing this or should i take to the engineering place and get them to do it. included is a file photo of what i am machining

[GDD]

Welder,

Cast iron can be easier to machine than steel. The removed metal comes away in crumbly bits and dust instead of strings of swarf. Downside is you can encounter very hard spots in some castings - a result of rapid cooling in those spots when the casting is made. Also, the dust is very abrasive and not good for machine ways (or lungs???) The bore you are enlarging has already been machined so less chance of hard spots as these are mostly on or near the surface of casting.

Graham

[pipeclay]

For starters is that a true representation of what you are going to machine.
I ask that because if it is what is the ID now.
Does the bore need to go all the way through the coupling.
How long are the Drive Dogs.

[welder]

pipe clay the bore as it is now is 20 mm and yes i have to bore all the way through it i am not sure how long the engine shaft is but the other side is already on a hydraulic pump i plan to drive so it should be right

[pipeclay]

If you are planing to bore all the way through what do you intend to do with the drive dogs.
I can see why you would have a problem boreing the coupling out,are you going to be using HSS or Carbide.
If HSS I would be running the Lathe at around 250/300 RPM and a feed rate around .004"/.008" and a depth of cut .060"/.120" for roughing.
I would leave about .020"/.030" for the finish,run around 400 RPM and a feed of .002"/.004".
If using Carbide I would run about 400/600RPM feed rate depending on nose radious and depth of cut depending on ridgidity of machine,once you get under the keyway you could probably up the speed,you may even be able to get bellow the key with your first roughing cut,the finish cut with carbide probably around 600/800RPM .010"/.020" depth of cut and a feed depending on nose radious.
Are you going to broach the key,do it in the lathe,shaper or slotter.

[Chas]

Welder,
Are you sure the material is cast iron? The Lovejoy Catalogue I looked at recently specified the standard coupling material as sintered iron, which I think may machine differently to cast iron. Be careful.

Regards,
Chas.

[welder]

just checked on there site it said it is made from sintered iron so how is that different to bore then cast iron and is it magnetic

[pipeclay]

It should if anything bore easier than cast,dont worry to much about what you have to do ,it will be virtually the same as boreing anything that your not to sure about.
Start off seeing how it cuts and work from there,the main problem if any you will have will be getting through the keyway.
How much machining experience have you got,you dont seem to confident.

[welder]

i have quite allot of machining experience just i have never done this type of metal i was originally worried about i cracking and splitting but i will give it a go wort thing that can happen i i stuff it up and loose $ 45 dollars but i will give it a go

[pipeclay]

It wont crack but I would be carefull as to how you approach the dogs,I wouldnt take to much off the ID if you pass through with the bar.
And dont forget to allow for tool spring.

[welder]

i am using a hss boring bar and will but the coupling in the 3 jaw chuck with the jaws of the coupling facing outwards

[pipeclay]

Are you sure that you will be able to get a boring bar to go into your bore with it set up with the Dogs on the outside.
If the bore is 20mm now and you are taking it out to 1.500" you will have to keep adjusting or changing your piece of HSS.
Are you going to use a Boreing bar or a piece of Solid HSS.
What way do you intend to machine the Bore without Cutting the Dogs.

[welder]

i am using a boring bare am will just keep on adjusting it also i don't have a set of dogs

[pipeclay]

The Dogs are your Drive Dogs on the Front of your coupling,from what I know you dont want to take any thing off these as you will give to much clearance on your coupling .

[welder]

sorry though you meant something else i don't need to machine them because i am adequate clearance if i machine them then the rubber spider will not fit right

[pipeclay]

Do the Drive Dogs sit flush at the moment at the End of your 20mm bore.

[Retromilling]

I don't think it is going to work very well machining from the dog side.
The dogs will get in the way of the boring bar shaft as far as I can see .
I think you are going to have to work out a way of holding it the otherway around .