Machining Hardened Steel Shaft

[jimbobbus3]

I'm trying to make a shaft extension for a countergear in a mower transmission. The shaft is about .700 diameter, unknown grade, and is haaarrrd. I tried using a solid carbide center drill, and it just laughed at me. I'll be the first to admit that I'm not experienced in working with hardened materials (hence my post here.)

The shaft carries several hardened and oil-impregnated spur gears on splines. Replacing the shaft outright isn't really an option, as I don't have any specs for replicating the splines. Ideally, I'd like to drill one end of the shaft to accept the extension, and then weld the two together. I'm not comfy just butt-welding the two shafts together, as I wouldn't expect to be able to maintain proper alignment during welding. I'd consider using a dowel pin to couple the shafts if I though I could make the necessary holes.

This is a short run. I only need to modify two units (or more depending on how many mistakes I make.) Do I need to grind off the hardened face of the shaft to expose machinable metal beneath?

Thanks,
J3

[DareBee]

It is hard to say which approach to take for machining.
I have good luck using square die drills and machining using a ceramic insert.

In my experience you DON'T want to weld an extension on. The old shaft is high carbon steel and at will go very brittle due to welding.
It is usually easier to make a coupling.
If that is not possible you will need to weld then anneal and then re-harden and likely straighten it.

[jimbobbus3]

Right now, all the solutions I've explored have been sub-optimal. I don't have facilities for heat treating. The end of the shaft is also a bearing surface - it bears against the cast aluminum case. Clamping to the outside of the shaft isn't an option for that reason alone.

I'll see if I can take a pic of the situation. Maybe a couple more sets of eyes will help find a non-traditional solution.

J3

[kalmah]

I've experience in hardened steel. I've try to use a center drill, but it doesn't work.
If your surface (where you want to drill) have a good surface finish, use drill for hardened tool steel without center hole.
Else try to grind or to mill the surface with radius end mill (designed for hardened tool steel).

Dijet, OSG, Mitsubishi, and other company have drill conceived for hardened tool steel.

Use a pecking cycle 0.25 x D
Feed rate = 0.01 x D
Vc = 20m/min

Good luck.

[jimbobbus3]

Okay, photos of what I'm attempting -
Photo1
Photo2

I've removed the stock input ring and pinion set, and I'm in process of making the countershaft become the input shaft - I need the input shaft parallel to the output driven axle. The countershaft has centers drilled from the original processing, but they're hardened. It's difficult to see, but the one is slightly burnished from my attempt with the carbide center drill.

Unfortunately, there's not a lot of meat in the aluminum case. I don't think I have enough leeway to open the bearing surface up much. Maybe I should consider grinding down the end of the countershaft and making a collar-coupler that has a keyway inside. Maybe? My power requirements are pretty low. The transmission is designed for 8-10hp vertical shaft engines. I won't have more than 1hp peak (1/4hp nominal) available, so I do have some latitude in terms of the necessary strength of materials and connections.

[Adobe Machine]

Use a "chop saw", lots and lots of water..you do not want the heat to bring the carbon to the surface .. cut back at least .08 to .100..
The big thing here is to keep the shaft cool when cutting.
You should be able to center and drill after cut.
Center drill the new extension for both the dowel pin and the live center.
Use an appropriate dowel pin for alingment and press halves together
Install on the lathe,cover the ways with newspaper and masking tape to protect those very valuable ways.
Use your 4 1/2 grinder with the lathe on "SLOW", work in a nice V between the extension and original part to the dept of the dowell, no more.
Clean up the grinding and the news paper, cover the ways with a fire-proof soft material ( I use my old welding jacket).
Dial indicate the shaft to your specs, should be .00001, use a soft hammer, be sure you pull the dial indicator shaft off the shaft when you gently hit the shaft. Will take awhile, unless your lucky..(doubtful), but you can bring to 0.
Pre-heat the area to be welded, if you have heat sticks, go to 450 degree while the lathe is in slow.
When your heated,shift lathe in neutral, spot , and immediatly spot 180 degrees away using the chuck to turn the shaft by hand.
Re-indicate, use torch to keep heat up while making an "attitude adjustment"
on the shaft.
Spot again, then immediatly 180 apart..
Do this two more times, indicate to 0.
You should be able to weld deep and hard,at this time ,then do a good cover pass.
Re indicate when hot, let cool and POST heat to 350 deg.
Let cool, I then use a positive rake diamond shape carbide insert on the weld to bring to size...should look brand new, no porosity..

This is how I have done it, it works, but I will say there are a lot of people on this forum that are better welders than me, so before you jump in to this, let some of the others comment , then you can form a plan..Have fun, be patient, make a plan before cutting and heating..

Adobe (old as dirt)

[pastera]

If you use Adobe's plan and arc weld - Make sure you're the weld current does not pass through the headstock! Connect the ground lead to the extension shaft as close to the weld as possible. You don't want to end up with a one-peice spindle bearing.

Aaron

[Adobe Machine]

Wow , in my pain drug induced coma I forgot that step..Arron is completly right..DO NOT USE THE MACHINE AS A GROUND...I really do not like welding on a lathe..some times it necessary..Tig is best, but MIG or stick is ok.
I also spray welding grease ( anti spatter) on the chuck, or any areas you can not cover .
Have a friend that builds precision drive shafts, has a 10 year old import lathe that has no weld spatter on it by using anti spatter, and they weld every day on it..I noticed the had made a ground clamp that fit around the larger drive shafts to avoid what Arron has mentioned.

Adobe (old as dirt)

[HuFlungDung]

Is there anything special about the extension? Is it just a piece of machinery steel like C1045 for example?

I'm not much of a fan of pinning extensions onto shafts. We weld 'em on solid right through to the center. We simply use an oversize piece for the extension, weld it on reasonably straight, and then 'machine it straight' after welding is all completed. I never arc weld in my good lathe But I do have various crude V blocks and stuff back in the welding room to position stuff like two shafts for a butt weld.

A simple V shaped (or U shaped if it is a large shaft) wedge prep on the end of each part is the preliminary step. This can be ground on pretty quick, cause nothing is hard to a grinding wheel I would fill in the center hole with weld at some point during this prep step.

Now, granted, the arc weld is going to draw out the temper a little too far on the hardened piece. You want it to, because you don't want the weld zone to be brittle hard. A small shaft like that will overheat pretty quickly with normal arc welding procedures, so I would not preheat it. But still, I would watch the amount of heat input to try to keep the colors from going too far up the hard shaft.

I'm more familiar with stick and MIG welding and I would stick weld this with 7018 x 3/32. It causes a bit more heat input than the MIG, but the MIG is almost too fast, and the quench effect of the cold parts is significant. Stick, because is it slower, will put a little more heat into the joint right on the initial passes, which is what you want to get a tempered weld zone. After the first couple of beads (on opposite sides of the V prep) you can begin to watch the heat buildup, and cool it with an air blast, not right down to cold, but enough to keep the high heat from travelling too far away from the weld area up the hard shaft.

[Chincia]

I have a question. Wouldn't it be easier to machine a whole new shaft with the extension as part of it?

No welding, centering, swearing, etc.

[Rich Carlstedt]

I did this so i know it works.
had to drill the end of a 4340 Rc 65 Shaft (like a dowel pin in hardness) and then cross drill it .
You will need help (hands)
You will need a drill press with balls (Used a Rockwell Industrial 1 to 2 HP).
The shaft had a center in it so center drilling was not an issue.
Clamped the shaft in a vise [vert] and put the vise in a large pan.
Put a ordinary Masonary (carbide tipped) in the drill press and set it for the fastest speed possible (3 to 4 K ?)
HAve someone pour from a can of water (we used a radiator spouted can) do not let up on pressure while drilling!.
Keep it steady and plenty of water .
The carbide will almost melt the material it gets so hot, but you need the water to keep the silversolder on the tip from coming loose (1100 deg F)
When you run out of water, IMMEDIATELY get out and refill the can.
Two job shops could not drill the shaft, and i had to do it during a break down with tools onhand.
A real carbide drill would have been nice, and holds size much better, but even a Masonary will work with enough pressure [ ! ]
My axel hole was 1/4" in a .875 shaft.
Then I filled the hole with mild steel rod and crossdrilled it 1/8".....for the crossdrill, I had to grind a small flat first.
If you do this, you can insert new shaft with pilot and lock it with a crossdrilled pin.simple.
Rich
by the way, the water prevents loosing the 'bearing surface too".... no tempering.

[Adobe Machine]

I have always been taught that most steels should be pre and some post heated for welding .If the steel is not preheated and post heated, after solidification, brittle behavior and cold cracking can occur. Most welding instructors agree that the weld mechanical properties IMPROVE with some pre and post heating:
( all these are ANSI steels )
1005-1023 shgould have a pre and post heat of 150 deg.
1035 depending on thickness +(-) 250, with a post heat of 1100 deg.
1040-42-43-45 preheat 350 to 450 deg, with a post of 1100-1250 degrees.
1050 pre heat to 350-450 deg, let air cool

1137 pre at 100, air dry
1140 pre at 200-350 depending on thickness, air dry

1330 ( Mag.) pre at 100 +
1340 ( Mag) pre at 200-350, post at 500 deg per inch of weld

4023 (Moly) 150 deg pre and 1100 post
4130 ( Ch Moly) pre At 400, and continue while welding
4340 (Ni Ch Moly) pre at 300, post at 300

I have a really long list that I took when I went to weld certification class,
( we had a big pending contract that required welding certs, so I had three of my welders and myself attend school), of the different steels and the requirement to pre-post heat.I've kept these notes for referance for 30 years now, and always required my welders/machinests to go by the book on pre and post heat.

We also did a lot of contract repair / machine work for CAT, and they required pre and post heat on a lot of their material.

Over the years I have gotten in the habit of pre and post heating most material, sure improves the weld, especially with MIG and TIG, where you need to machine after.

Adobe (old as dirt)