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Appropriate steel for a spacer?

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Siggi

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#1
Hey y'all,

I'm restoring an old 14" Rockwell/Delta metal/wood cutting bandsaw, which has a crack in the casting. After some consideration, I've figured that the safe thing to do is to machine a new spacer for the one I believe is short to protect the casting from getting crushed (again) when the wheel is tightened up.
I have a PM1236 lathe in my basement, but I'm a rank beginner, and so I'm pondering this very basic question of what sort of stock would be (most) appropriate for the application. This spacer rests against two inner bearing races and rolls with the shaft. The cavity in the casting has oil in it, that'll splash around when the big gear wheel spins.
So, can y'all elucidate me as to the whats and the whys?

Siggi
 
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dlane

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#2
A pic would help, of casting crack and where spacer will go, also the saw.
 

Siggi

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#3
A pic would help, of casting crack and where spacer will go, also the saw.
The original thread has a picture of the crack, which I've now sealed with JB weld to prevent oil leaking out at least. Here's the shaft with the full stack-up on it, the existing spacer is poking out of the end by the gear wheel.
IMG_20180417_073348.jpg
I believe the casting cracked because the spacer is about 65 thou short, and so when the wheel is tightened up with the nut that goes on the left side of the shaft, the shaft ends up pulling on the casting from the snap ring on the right-hand bearing. When I dry assemble this, I get about 65 thou axial play on the big gear wheel, and at one end of travel it'll rub against the casting.

Here's a couple of pictures of the spacer.
IMG_20180417_073405.jpg IMG_20180417_073416.jpg
I essentially need to reproduce this piece about 65 thou wider.
 

Nogoingback

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#4
What's the old spacer made from? If it's steel, I imagine anything would work: 1018, 1144, whatever. If the spacer just locates the inner
races of the bearing relative to one another, I doubt Rockwell used anything exotic.

EDIT: I was typing while you were posting your pics. It looks as though your spacer has a shoulder, or am I seeing it wrong? Is the spacer
located between the two bearings? It's not completely clear how the assembly goes together. But, again, if the spacer is simply located
between the bearings and rotates with the inner races on the shaft, the material probably isn't critical. Or, is there more going on here?

While taking up some play in the shaft may be needed, it may not be a good idea to spacer it to the full distance of .065" . Most assemblies
require some end play to allow for expansion due to temperature change during operation.
 
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markba633csi

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#5
Hi Siggi I feel your pain, JB weld is a good remedy for the moment until you are able to have the crack veed out and brazed for
a more permanent repair
For a spacer any mild steel would be fine- even aluminum would work also I think
Mark
 

francist

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#6
Wonder if you could just make a washer of the appropriate thickness to use along with the existing spacer? Might be less effort and you could try one or two different thicknesses if you were uncertain about the take up distance required.

-frank
 

pacifica

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#9
I also would use 12L14 or 1215, free machining and great for a beginer since it cuts like butter but still is strong, especially compared to 6061 aluminum.You can find both at MSC. Look for free shipping since metals are expensive to ship.
 

Ray C

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#10
In all honesty, I cannot visualize how that part fits (or mis-fits, as the case may be) to cause the housing to crack as shown in the pictures related to this thread.

The big gear has helical teeth and such a gear will always place an axial thrust on the shaft it spins on. Are you absolutely certain that the cracked housing is because of the deformed or altered spacer you intend to make? Is it possible the axial forces are excessive for some reason? Are you certain this was assembled properly? Maybe something is in there backward...

My thought is to proceed cautiously until you absolutely understand the failure mechanism.

If you proceed on making that part, since you probably cannot measure precisely how big you want it to be, I'd recommend making it more than 65 thou bigger. This way, you can trim it down if necessary.

Ray
 

dennys502

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#11
I agree the stackup on the shaft makes no sense.
The 2 dogs are not meshing with anything - and the spacer looks like it would fit over one of the dogs. Just hard to tell how it is assembled from the pictures.
It looks like the crack is from compression not torsion. Like something was assembled wrong and tightend down.
 

GL

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#12
I agree with the use "steel" crowd, especially if it is hard (file test would tell that story). If it works like we think, the spacer is compression loaded. As suggested by francist, using shims may be a better path. In general, cast housings don't crack in general use. Something moved that wasn't supposed to (wear), something stopped fast (crash), or things got loaded heavy for awhile. What does the bottom of the hole this sits in look like? As a group, we often buy used equipment we don't know the history of, or who or how good the last guy was that messed with it. Not likely Delta/Rockwell missed it by 0.065. It is a helical gear, so shaft/spacer could see some thrust load. You said it runs in oil, what happens if the oil isn't there? Who rubs on who (maybe for 65 thou)? You are looking at parts we can't see.. But no one who gets into this hobby/interest/obsession is a mechanical idiot - noob or otherwise, you already tore into something way deeper than most would. Good luck with the quest.
 

GoceKU

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#13
If you have a register where this spacer pushes against, your best bet is to make couple of spacer shims so you can allow some endplay so it want seized and is probably what is missing, manufacturers often use them to set the endplay and allow for future adjusting as the machine is being used.
download (1).jpg
 

Siggi

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#14
Thanks everyone for the advice, here's a diagram of the assembly from the instruction guide on Vintage Machinery:
Stackup.png
What makes sense to me is for nut (#140) to tighten the wheel (#141), the inner race of the bearing (#143), the spacer (#149), the inner race of the large gear wheel's bearing (#151) against the retaining ring (#153).
Since the big gear wheel rides on a bearing, I don't see why you'd need axial play there (but I'm willing to learn).
As-is, when nut (#140) is tightened, it'll pull the opposite side's bearing (#158) into the casting and crush it. Note that this casting is hollow, with fairly thin walls (1/8" maybe), which is different from the woodcutting model, where I believe the spindle goes through a bore solid through the casting.
I also don't think it makes sense for the big gear wheel (#150) to rub against the casting at one end of the axial play.

Note that there's a double clutch on the shaft to switch between direct drive for wood cutting through pulley (#160), to metal cutting through the gearbox and the big gear wheel (#150). When disengaged, the pulley will idle on a bushing (#161 - which I'll have to replace, oilite ordered), and when engaged, the gear wheel will idle on the bearing (#150).

EDIT: I was typing while you were posting your pics. It looks as though your spacer has a shoulder, or am I seeing it wrong? Is the spacer
located between the two bearings? It's not completely clear how the assembly goes together. But, again, if the spacer is simply located
between the bearings and rotates with the inner races on the shaft, the material probably isn't critical. Or, is there more going on here?
Yes, the spacer is steel, and it's located between two bearings. There's a shoulder on the shaft, as the IDs of the two bearings are different, and so there's a step in the spacer bore.

The big gear has helical teeth and such a gear will always place an axial thrust on the shaft it spins on. Are you absolutely certain that the cracked housing is because of the deformed or altered spacer you intend to make? Is it possible the axial forces are excessive for some reason? Are you certain this was assembled properly? Maybe something is in there backward...
Yeah, I don't know the history of this bandsaw, except that it's led a hard life. It was covered in chips-in-cutting-oil and sawdust when I got it, the bottom of the base was quite rusty, the big pulley was quite corroded and the keys in the step pulleys were out of place - one of them pushed all the way up the shallow of the keyway and nearly rubbing on the casting.
One thought I had was that the bearing was installed inside-out. This bearing has an inner race that's wider than the outer race, and offset to one side - by just about 65 thou.
I don't think this makes sense however, as the shielding on this bearing gives it an orientation for "outside", plus there'd have to be a spacer on the outside of the bearing to locate the wheel correctly...
 
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FOMOGO

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#15
Depending on the diameter, you may be able to source existing valve spring shims to accomplish what you need. Pretty much everything that turns is going to require some end play, 3-5 thou should do it. Agree that brazing up the crack is the right way to go, but even if you stick with the JB solution, I would drill out both ends of the crack to keep it from spreading. Mike
 

Nogoingback

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#16
The diagram shows 2 parts (149 & 152) between the bearing in the housing (143) and the bearing that supports the large gear (151). You have one.
The parts list
shows 149 as a spacer and 152 as a retainer nut which appears to secure the bearing (151) into the gear. Is that retainer installed in the gear?
If it's missing, then you may have a shop made part fabricated to replace 149 and 152. The other option is that someone lost the spacer along
the way and made a replacement, but dimensioned it wrong.
 

Nogoingback

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#17
One thought I had was that the bearing was installed inside-out. This bearing has an inner race that's wider than the outer race, and offset to one side - by just about 65 thou.
To which side was it offset?
 

Siggi

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#18
The diagram shows 2 parts (149 & 152) between the bearing in the housing (143) and the bearing that supports the large gear (151). You have one.
The parts list
shows 149 as a spacer and 152 as a retainer nut which appears to secure the bearing (151) into the gear. Is that retainer installed in the gear?
Thanks, the retaining nut is in place on the gear. It rotates with the gear and the outer race of the bearing, while the spacer slips through it and rotates with the shaft, so I think that's all working as intended :).

The other option is that someone lost the spacer along
the way and made a replacement, but dimensioned it wrong.
Yeah - that's another possibility.

To which side was it offset?
It was offset to the outside, which I think is the orientation it's designed for, as that provides spacing for the cast aluminum wheel away from the bearing shield and the outer race. Also the bearing has the shielding on the side where the inner race protrudes, which is consistent with "outside".
 

Siggi

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#19
Interesting, by my measurements the spacer would be 3/4" on the dot to pick up the play on the shaft. Surely that's not a coinkidink?
 

Nogoingback

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#20
It sounds as though you've figured out what you need. A steel spacer made from whatever you have on hand sounds
like it would solve your problem.
 

Siggi

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#21
So, I turned a new spacer, made it 3/4" thick on the nose. Found that there was no way to assemble the damn thing with a spacer that size, there was just no way to get the large gear wheel into place in the casting cavity. I figure the spacer and gear wheel were probably 65 thou too thick to get into place, go figure :).
So, I figure Rockwell/Delta must have known what they were doing, so I'm assembling it with the old spacer in place. I'll be gingerly tightening the lower wheel, and only once the gearbox is in place.
We'll see what happens...
 
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