What material for shafts?

[hennebury]

Hi, So I am rebuilding woodworking machines. I often have old Maka mortisers to rebuild.
The mortising head unit is held in a cast iron unit with two 30mm bores, the unit slides on 30mm round bar. The cast iron bore and the round bar are often galled up, sometimes quite badly. I would like to replace the round bar with a slightly oversized bar and hone the cast iron bore to get a good clean slide.
I don't know what type of material the bar is made from. It doesn't appear to be very hard.
Can anyone shed some light on what would be a suitable replacement round bar for this application.

 

[lucky7]

By any chance is the OP the guy who rebuild a Martin T17 recently? Is yes, much respect.

L7

 

[hvnlymachining]

I would go with 4140 prehard. It's tough, decent hardness, machinable and easily aquired.

We use literally tons of this stuff for the local sawmill in nearly all round bar applications due to it's durability.

 

[deltap]

Consider stressproof 1144 ground.

 

[hennebury]

By any chance is the OP the guy who rebuild a Martin T17 recently? Is yes, much respect.

L7

Yes, and thank you. I recently did a Martin T17 rebuild.

 

[hennebury]

I have to machine a step down on the end to press-fit into the casting, this is what will make me nervous. I have seen one or two with cracks, so any advice on how tight to do this, and any tips on pressing the shaft in without cracking the casting, heat the casting? cool the shaft?

 

[hvnlymachining]

Press fit interference depends on diameter, I usually run with the .00075" per inch of diameter rule, but there are a lot of variables to consider. Directional forces are one, materials are another. Cast iron doesn't like being stretched and even cooling around a shaft causes stretching stresses. I would err on the side of caution and go more like .0005 per in interference and use heat on the casting and cool the shaft for assembly.

1144 is easy to machine, I have no idea how it wears against cast since it is in essence a "semi steel" and is closely related to cast iron.

4140 is a tool steel and wear resistant, but harder to machine.

 

[cyanidekid]

Press fit interference depends on diameter, I usually run with the .00075" per inch of diameter rule, but there are a lot of variables to consider. Directional forces are one, materials are another. Cast iron doesn't like being stretched and even cooling around a shaft causes stretching stresses. I would err on the side of caution and go more like .0005 per in interference and use heat on the casting and cool the shaft for assembly.

1144 is easy to machine, I have no idea how it wears against cast since it is in essence a "semi steel" and is closely related to cast iron.

4140 is a tool steel and wear resistant, but harder to machine.

1144 is not "semi steel" "closely related to cast iron" (agree with comments on cast iron tho)

if it is a linear bearing surface that is often encountered in a galled state, why not get chromed hydraulic rod? alternately, "Thompson shafting", or any quality brand of linear motion shafting.

 

[Garwood]

1144 is not "semi steel" "closely related to cast iron"

Stressproof is super strong, but it machines like cast iron and it has the same damping properties as gray cast iron. I don't know what the molecules look like compared to cast iron, but I'd liken stressproof to cast iron moreso than steel.

 

[cyanidekid]

Stressproof is super strong, but it machines like cast iron and it has the same damping properties as gray cast iron. I don't know what the molecules look like compared to cast iron, but I'd liken stressproof to cast iron moreso than steel.

1144 is STEEL, NOT cast iron, not related to cast iron, not even remotely alike. what the hell are you guys talking about???

"machines like cast iron" hum.. don't know how much cast iron you have worked with, but some ive come across is harder than glass and destroys carbide tooling in short order, (10 hrs in the HT furnace per inch usually fixes that), 1144, NEVER.

some has so much graphite it turns to a grey dust with no discernible chip, 1144, NEVER.

 

[mhajicek]

4140 prehard is easy to machine with carbide, and leaves a good surface finish.

 

[Overland]

Hydraulic cylinder rod is ground, chrome plated, easily machined, readily available in stock sizes.

 

[Garwood]

1144 is STEEL, NOT cast iron, not related to cast iron, not even remotely alike. what the hell are you guys talking about???

"machines like cast iron" hum.. don't know how much cast iron you have worked with, but some ive come across is harder than glass and destroys carbide tooling in short order, (10 hrs in the HT furnace per inch usually fixes that), 1144, NEVER.

some has so much graphite it turns to a grey dust with no discernible chip, 1144, NEVER.

There is no steel that has the same characteristics as 1144. It acts just like cast iron. Steel rings. 1144 doesn't. 1144 is great for tooling, arbors, machine parts because it dampens like cast iron does.

 

[Modelman]

Hydraulic cylinder rod is ground, chrome plated, easily machined, readily available in stock sizes.

The trade name for this stuff is TGP, Turned, Ground, and Polished. It is available in 1144, 1045, 4140, and at least one of the stainless steels. It is available chrome plated, but is easy enough to machine if you start from the end to get under the plating. It's available in a bunch of fractional and metric sizes. IIRC, typical diameter tolerance is +000/-.002.

Dennis

 

[eKretz]

The trade name for this stuff is TGP, Turned, Ground, and Polished. It is available in 1144, 1045, 4140, and at least one of the stainless steels. It is available chrome plated, but is easy enough to machine if you start from the end to get under the plating. It's available in a bunch of fractional and metric sizes. IIRC, typical diameter tolerance is +000/-.002.

Dennis

Oh no it's not. The cylinder rod/Thompson shafting is another animal entirely. It would be perfect for this application. It's chrome plated and induction hardened. Super hard layer on the outside periphery that basically amounts to a case hardened surface under the chrome. It would be my choice for this application if the old stuff was galling up for sure.

As for 1144, it may dampen a bit better, (don't quote me on that, I'm relying on Garwood's description here, I've never noticed that) but it doesn't short chip in my experience, so I wouldn't say it's just like iron. And while some irons are hard (I'm looking right at you, chilled cast iron) that's due to properties that were manipulated to make it so, just like steel can be heat treated.

 

[hennebury]

Thanks for all of the input. So I have to replace some piston rods for the feed cylinders as they are also a mess, for those i was going to order 25mm the induction hardened, chrome plate cylinder rod. If there is no reason not to use the cylinder rod for the linear rod on the cast iron feed unit, I will use that there also.

 

[cyanidekid]

I just don't know what sort of "1144" stock you have come across, but please look it up. it is JUST STEEL. no "magical cast iron like properties".

"steel rings, 1144 doesn't" , well the pieces I just pulled from the rack ring quite nicely...

 

[cyanidekid]

Oh no it's not. The cylinder rod/Thompson shafting is another animal entirely. It would be perfect for this application. It's chrome plated and induction hardened. Super hard layer on the outside periphery that basically amounts to a case hardened surface under the chrome. It would be my choice for this application if the old stuff was galling up for sure.

As for 1144, it may dampen a bit better, (don't quote me on that, I'm relying on Garwood's description here, I've never noticed that) but it doesn't short chip in my experience, so I wouldn't say it's just like iron. And while some irons are hard (I'm looking right at you, chilled cast iron) that's due to properties that were manipulated to make it so, just like steel can be heat treated.

mostly agree e, but its NOT usually anything that was intentionally done to cast iron that results in shitty unworkable cast, usually its a sin of omission. not slow cooling, for one results in the white glass like state in thin sections, and a bad mix of charge that includes aluminum, titanium etc results in the oxides and carbides of those in the casting. those cause hell when machining.

 

[eKretz]

mostly agree e, but its NOT usually anything that was intentionally done to cast iron that results in shitty unworkable cast, usually its a sin of omission. not slow cooling, for one results in the white glass like state in thin sections, and a bad mix of charge that includes aluminum, titanium etc results in the oxides and carbides of those in the casting. those cause hell when machining.

Guess you haven't run up against my #1 enemy. I used to have to turn chilled cast iron rolls now and again as an apprentice. It is godawful nasty hard stuff. Couldn't touch it with carbide. Finally got some 1" diameter ceramic button inserts. Those ate it up at a surprisingly low cutting speed, throwing red hot ribbons up in the air like confetti and making a noise somewhat akin to how I'd expect a banshee howl to sound. I lit quite a few brooms on fire trying to contain the chips a bit.

Your description includes "not slow cooling" which is basically how chilled cast iron is made, albeit intentionally. All white iron. Blechh. And yes, hell when machining is a very apt description. I do understand that it can occur spottily and accidentally in poorly controlled casting conditions. If you think that's bad, imagine a whole solid chunk of the stuff!

 

[Modelman]

Oh no it's not. The cylinder rod/Thompson shafting is another animal entirely. It would be perfect for this application. It's chrome plated and induction hardened.

You can get induction hardened TGP that's also chrome plated. I didn't mention it because I thought he has to turn reduced diameters on the ends, and the chrome plating should be enough to stop the galling, but I will admit, the harder skin under the chrome will make it more resistant to being dented if hit by something.

Dennis