Reaming a 1/8" bore to about 2 1/2" deep

[DickDastardly40]

I am tossing a few ideas about regarding manufacture of a built up type 3 throw crankshaft using a mixture of threaded and silver soldered pieces. I am wondering if I can support the elements of the 3/8" dia journals on a 1/8" rod while assembling. I would then withdraw the rod to prevent having to cut out the crank throws.

Whether this would be easier remains to be seen however, to get a decent set up I will have to drill through the journals (possibly from either end) and ream to size.

A hand reamer is tapered for the first 1/3 of its length and you cannot ream deeper than the cutting teeth due to the shank. Going from either end would leave an unreamed portion in the middle.

I have never used a machine reamer but they look as though the teeth are proud of the shank so would possibly be suitable for deeper work so I could go through in entirety from one direction.

I would appreciate the following advice if anybody knows:

The suitability for what I propose
The speeds at which they should be used
I know they are parallel, is any lead in required?
How much undersize should the job be drilled before use?

Thanks is advance for any replies.

Al

 

[Mainer]

A machine reamer will go through -- the shank will be slightly smaller than the reamed diameter. No lead-in required. For an 1/8" reamer, I'd go about 0.003" undersize for the starting hole. Personally, I like the spiral-flute reamers. Run about 250 rpm, probably, with cutting oil. Check for chip build-up and clear the hole periodically if you need to (you may not).

For a deep hole, you may have trouble keeping it straight -- the drill may wander when drilling the starting hole -- so I'd suggest paying close attention to that possibility when drilling, to try to minimize that.

 

[kvom]

I'll just repeat what I was told in class:

Pilot hole 1/64" smaller than final, oil on reamer, and continuous feed (e.g., don't stop in the middle).

 

[Mcgyver]

as an overall strategy i'm a little iffy on it if you aren't planning on machining it afterward....and if you are machining a crank made from solid is imo easier. combination of the clearance required for SS, things moving a bit when heat and 1/8 dia not having that much rigidity, there will be some clearance between the 1/8 rod and hole and who's to say how straight the 1/8 bar is and the biggy; its tough to get a 1/8 hole straight for that distance to any kind of tight tolerance....I've not done it this way so can't say it won't work, but I'd be concerned about those items...i have done one from solid and it wasn't too bad...although how feasible that is depends on the size of it

if you want to do built up, consider interference fits (press or shrink) or easier still loctite. With loctite you can have a very close fit and it will still work whereas with SS you need a couple of thou clearance

 

[kf2qd]

An 1/8th rod is not going to be very rigid, which is the whole reason behind building a crank from a solid shaft and then cutting it out at the rod journals. You would be better off making a fixture from solid blocks with a 3/8ths reamed hole and cutting it away where the journals will be and using it to silver solder a crank. The reason behind building from solid is for fixturing, not just to make it difficult.

 

[Mainer]

I think I'd hesitate to leave 1/64" to take out with a 1/8" reamer. The flutes on a 1/8" reamer are pretty small. It could probably be done, but I think you'd need to clear chips frequently.

 

[DickDastardly40]

Thanks for your input so far gents.

Looking at this last night in reality rather than just thinking about it, I experimented with 1/8 which as McGuyver mentioned looks a little small as did 5/32 but I got moaned at to come indoors before I could go to 3/16. Obviously bigger is easier as the drill and reamers are longer. (hand reamers dont have chucking reamers yet)

I think I've got a 3/16 reamer. I was intending to use silver steel drill rod as i have some 13" lengths in various diameters all seem straight when rolled on the plate. The reasoning behind a fabricated crank is so as not to make split eccentrics. If it doesn't work never mind, the beauty of a scratch build is you do it how you want to try it.

I'll post on how it turns out in due course (please no-one hold your breath)

Al

 

[tel]

Breath not being held, as per instructions.

 

[raym 11]

Has anyone tried turning the lathe (chuck) by hand whilst feeding the reamer with the tailstock? Works for me. Using larger reamers with a center hole (the reamer was originally ground on this center) in the shank I use a center in the tail stock, attach a tap handle on the shank (it leans on the cross feed to keep the reamer from turning). I then feed the tail stock and turn by hand. I apply cutting fluid (kerosene) with my third hand.
I usually end up with round holes to size . I've used this method on aluminum and
brass/bronze.

Ray M

 

[Peter Neill]

Coming a little bit late to this, as I don't get on here often enough, but I though I'd add my twopenniesworth.

I've currently been reaming 2.5mm holes for piston gudgeon pins for parts (on the contentious piston/bore clearances thread).
I drill the pistons 2.3mm and then ream to 2.5 afterwards, so leaving around 8 thou' to come out with the reamer. The machine reamer used is around 3.5"-4" long, so plenty of length for what you need, and the shank is definitely smaller than the flutes. I'm running at around 900 rpm, and the feed through must be continuous without stopping.

A couple of thing to remember. The reamer will always follow the drilled hole, so if the drilled hole is not straight, neither will the reamed hole be.
Also, brand new reamers always tend to cut a tiny fraction oversize. My 2.5mm holes come out pretty religously on size at 2.52, whether it's in bronze, cast iron, or steel.

Peter