how to go about a bushing

[marcofsiny]

Its been a while since I've been here. I havent done anything with metal on the lathe since last time I was on here. Some wood turning but thats it.
I have a question about turning a bushing on the lathe. This is what my project is going to be for....I have a flywheel (?) that fits over the shaft of a small motor for a scroll saw. The motor is shot. I ordered a totally different motor and need to make the flywheel piece fit the shaft of the new motor,,which I'm not sure of the size yet but it could be 5/16".
The flywheel's hole or the old motor shaft measures 10mm with a digital caliper. So,,I'd like to make a 10mm o.d. bushing with a 5/16" hole so that I can reuse the old flywheel. (the saw is direct drive).
What is the best and easiest to work with type of metal I should use as a bushing? (my skills are below amatuer). I thought aluminum would be easy for me to turn but would it hold up as a bushing? Any tips on making this will be appreciated,,,but I am very limited on tooling,,I did just pick up a 5 piece center drill set for this project.
In the pic,,,you can see the hole on the left that I will need the bushing for. The old motor is on the right. The flywheel is a press fit with no set screw to hold it to the shaft.

[Inspector]

Well if the old motor is just going for scrap anyway why not cut the shaft off and bore a hole in it to match the new shaft size? Removing the old motor's end cap and cutting with a hacksaw, inside close to the windings etc., will give you enough straight material to hold in your lathe chuck I would think.

Pete

[Harold_V]

One word of caution.
If you intend to create a press fit, you're going to struggle considerably if you rely on a caliper for measurements. They're not capable of providing the degree of precision required, especially if you use both inside and outside jaws, which rarely agree with one another. The difference of only .0005" equates to a fit that goes from a press to a slip fit in that size. I fully expect your caliper won't be able to discern even a thou, let alone half of one.

Do not rely on drilling or reaming if you hope to have the bushing control the alignment of the installation. The slightest deviation from center will result in the fly wheel running off, and the chance of doing so far exceed the chance it won't.

Using a piece of material that permits gripping without interfering with the overall length, drill the bore undersized, and rough the OD, taking both within .03" of finish size. Keep close watch on temperature, as a few degrees will shift the real size, so the expected size won't be true. Take both inside and outside to the desired diameter, taking three equal depth passes. That means you must bore the hole.

My recommendation is to measure with a micrometer, as well as a small hole gauge. The bushing, I assume, will have a relatively thin wall, which is just fine, even with aluminum. All it does is act as a spacer, as both surfaces should be under compressed condition when assembled. I would probably recommend the use of a good machining steel, however, something like 12L14, or even Stressproof. That would eliminate any doubts you may have.

I'd recommend you make the bushing a snug slip fit in the bore, and a half thou press fit on the shaft. That way, when the units are combined, the half thou press will cause the bushing to expand slightly, creating a press fit for the components. Do not part the bushing from the stock until it is completed. That way you won't alter concentricity. You should be able to part the bushing to length, with no need to face the parted portion.

If you find that the bushing is free to move when you attempt assembly, you may have to reverse the fits, or you may have to create a shoulder that prevents the bushing from moving when the items are assembled. A little thinking can resolve the problem, which would be difficult to discern without having the components in one's possession.

You can do it. Just don't do stupid things like expect a drilled hole, or a reamed hole, to be adequate. It most likely won't be. However, if you MUST ream, bore first, to establish concentricity and parallelism. Ream only a few thou, no more than .005", which will help assure size.

Harold

[Harold_V]

Well if the old motor is just going for scrap anyway why not cut the shaft off and bore a hole in it to match the new shaft size? Removing the old motor's end cap and cutting with a hacksaw, inside close to the windings etc., will give you enough straight material to hold in your lathe chuck I would think.

Pete

Not a bad idea, although I fully expect that the end result will be a fly wheel that doesn't run true. If a little wobble doesn't matter, it would work.
Remember, a half thou out of perpendicular at the bushing may equate to several thou at the outer edge of a flywheel. A person is best served making the bushing in one setup, depending on what is expected from the assembly upon completion.

Harold

[Mr Ron]

If after making the bushing as per Harold's recommendation, it is a loose fit, use some "loctite". That will save you from making another one.

[revrnd]

If after making the bushing as per Harold's recommendation, it is a loose fit, use some "loctite". That will save you from making another one.

Loctite 609 Bearing Retaining Compound is good for this.

[Inspector]

Not a bad idea, although I fully expect that the end result will be a fly wheel that doesn't run true. If a little wobble doesn't matter, it would work.
Remember, a half thou out of perpendicular at the bushing may equate to several thou at the outer edge of a flywheel. A person is best served making the bushing in one setup, depending on what is expected from the assembly upon completion.

Harold

The reason I suggested using the old motor shaft was because between the picture and the description of a press fit to the flywheel, I assumed there was a taper fit between the two. Not having to contend with making a taper would make things a little easier given his admitted experience. Much like mine. I'd still salvage the old motor shaft for the bushing rather than trying to find a short length of steel for the bushing. Price is right.

Pete

[marcofsiny]

thanks for the suggestions. I did plan on using bearing retainer if there was a slight loose fit. I had to use it in a pulley once and its still holding up.

Ok,,,my project hit a big snag. The motor came in the mail today. The shaft is larger than I expected,,the other motors for similar tools was 5/16".
I have no clue what the measurement is. Using my digital caliper (all I have),,I got .475 inch and 12.07mm ,,if I squeeze harder or eaiser it changes. When I looked up decimal to fraction charts I dont see see these two numbers anywhere. I will have to guess that it is a 12mm shaft?? this is what I bought : Delta Motor p/n 1347414
Any idea what I should do now?

[Harold_V]

Ok,,,my project hit a big snag. The motor came in the mail today. The shaft is larger than I expected,,the other motors for similar tools was 5/16".
I have no clue what the measurement is. Using my digital caliper (all I have),,I got .475 inch and 12.07mm ,,if I squeeze harder or eaiser it changes. When I looked up decimal to fraction charts I dont see see these two numbers anywhere. I will have to guess that it is a 12mm shaft?? this is what I bought : Delta Motor p/n 1347414
Any idea what I should do now?

Yes, you should acquire a 1" micrometer. If you work with such things even occasionally, it will be a good addition to your shop. You need not spend a lot of money. A cheap Chinese micrometer will be a quantum leap better than the use of one of the best calipers on the market.

The shaft on pretty much any motor will NOT be nominal. They are purposely made undersized, although I can't detail how much, as I'm sure it varies. It is also possible that the shaft is a bastard size, which is not all that uncommon in industry, so one can't procure off-the-shelf components to make repairs. By using proprietary components, the maker holds you hostage.

With the proper measuring instruments, so you can determine what size you really need, you most likely will be able to open the bore of the flywheel (by boring, not drilling). Dial it true, using a four jaw chuck. It will run only as true as you make it in the setup.

Harold

[marcofsiny]

I just looked up one on HF. I'll try picking it up before the weekend. I see what your're saying about companies making parts that only fit their stuff.
There is a boring bar that came with the lathe,,I have to look at it again...I'm not sure of the diameter.
Is boring used to creep up on a measurement? I was wondering if the bore is a tad over 12mm,,,,would I be better using a 12mm drill bit and then creeping up to the measurement?


edit: my boring bar is too big to fit the hole. recommend anything? diameter of one?

[choprboy]

If you are going to get the HF micrometer, I would suggest you do not get the "0-1 Mechanical Micrometer". I found it to be a piece of garbage, the internal mechanism keeps binding/freeing and giving inaccurate readings on the counter. The digital micrometer seemed OK, though occasionally would be a little flaky. The regular old micrometers seemed to work fine, though after picking up some Starett and Mitutoyo micrometers locally off CL for ~$15-30 each, the HF mostly sit in the drawer. I use my HF dial calipers for quick measuring all the time though.

For the bushing... my preferrence would be for steel, second choice brass, I think I would shy away from aluminum for something so small. Personally, if I was doing it I would make the bushing OD a 1-2 thousandths oversize, the ID a suction fit with a slight corner bevel. Once finished I would freeze the bushing with dry ice and drop it into the bore, it will lock in place as the temp comes back up. Depending on how tight you want it on the motor, I would then either reamer the ID to finished size and press it on or freeze the motor shaft and insert it into the bush. That would be my preference anyways...

[Harold_V]

A two thousandths press fit on a bore of that size isn't reasonable. You'd have issues with assembly, even when heating or cooling. In fact, if the flywheel is cast iron, one runs the risk of splitting. A half thou press is more than adequate, assuming it truly is a half thou. For the record, cast iron is not known for its tensile strength, although it has considerable compressive strength.

In regards to a boring tool, there's no reason in the world why you can't fashion one from a piece of HSS. I've hand ground such tools all my life, as it's very much a part of being a machinist.

When you intend to bore, roughing the hole with a drill is acceptable, but don't get too close to finish size, as drills often don't generate round or straight holes. You need enough material remaining to take a skim cut, take the hole to a round condition, and have enough material remaining to take at least one more pass, to take the bore to size. However, wise people take such cuts in three steps. When you know the approximate size of the hole, the first cut is 1/3 of the remaining material, which rounds the hole. The second cut is the second third of the remaining material, which should duplicate cutting pressure of the last cut (the balance of the material). After the second pass, measure the hole (small hole gauge), then take the balance of the material with the third pass, which should take the hole to finished size.

Cast iron, assuming it's not chilled, should machine very freely, although it's messy (free carbon). You should be able to trust the dials to achieve size. If you mess up and end up too large, there's always Loc-Tite, although my choice is to avoid its use. With that said, if the hole requires being enlarged, I'd choose boring over drilling when there's little material to be removed, as I suspect there is in this case.

For ease of grinding, you would likely be served well enough starting with a ¼" square, although my preference is typically larger. If you have a question about what the tool might look like, I can post a picture of such a boring tool, and provide some basic guidance for grinding.

Harold