Little Wonder

[Trevor Thompson]

So far I have made 6 wheel "blanks". Numbers 7 and 8 in the lathe:

I have cut that long chunk of steel into shorter lengths to hold securely in the lathe. I like to turn the face, bore (and ream) the axle hole and finish the tread and flange to size in one go so everything is truly concentric. Then turning the blank around do the same on the other end. You can see that the inner end is already machined in the photo.

What I seem incapable of doing is parting off 40mm diameter steel without causing huge chattering. I have followed all of the on line videos - but I still can't do it successfully. So its back to the hack saw:

When it's cut off I will hold it in the lathe on its tread, using the flange to locate it, and clean up the inside to get the flange thickness right.

Of course these wheel blanks are really partly machined wheels rather than blanks. They will need mounting in the rotary table for drilling the holes for the crank pins, and milling out the gaps between the spokes. At the end I will mount the wheels in a mandrel on the lathe to form the tapers on the flanges.

Trevor

[GTB]

What I seem incapable of doing is parting off 40mm diameter steel without causing huge chattering. I have followed all of the on line videos - but I still can't do it successfully. So its back to the hack saw.

I don't think any of the common model engineering lathes are rigid enough, or powerful enough, to part off 40mm BMS......

My 7" x 12" lathe draws the line at about 1/4" in steel and about 1" in brass and then only with a 1mm parting off tool. The 12" swing toolroom lathe I had in my laboratory early in my career would walk through 2" steel bar using a 3mm parting tool without changing note. The modern equivalent of that toolroom lathe is now made in Taiwan, costs about A$7000 locally and weighs about half a tonne.

My standard rolling stock wheel is turned from a disc of 1.25" BMS. Just after I got my lathe, I was about 20% of the way through the first cut for my first wheel blank using a hacksaw when I said "******* this". I climbed in the car, drove over to Hairy Forbes in Dandenong and came home with a chinese made 6 x 4 metal bandsaw. I was lucky, the anonymous worker who assembled mine knew his stuff and I got one that can cut square within 10 thous. on a 2" cut. It's on it's third blade and still cutting square.

That bandsaw has now cut something north of 300 wheel blanks and considering the cost of commercial wheelsets, both it and the lathe have paid for themselves just making wheels. The cut is square enough that I only need to skim off about half a mm from each face then drill and ream the blank ready for mounting on the mandrel. I can usually face both sides of one disc while the bandsaw is knocking out the next one. It has also saved over a metre of steel bar, as I would have to cut the blanks to 12mm wide if I was using a hacksaw. I'm not that good at cutting straight with a hacksaw.

From my point of view the bandsaw was well worth it. My health isn't up to cutting wheel blanks with a hacksaw.

Graeme

[Trevor Thompson]

Graeme

Thanks for the encouraging response - it was what I hoped I might get as a result of describing hand sawing it off!

I was wondering if the lathe was insufficiently rigid for parting off like this - and you have confirmed that thought for me.

I can part off brass properly with a 2mm wide cutter on it - and it feels controlled and safe.

I had dismissed a mechanical hacksaw as taking too much room - but I will think about a band saw.

Thanks

Trevor

[GTB]

I had dismissed a mechanical hacksaw as taking too much room - but I will think about a band saw.

Unlike power hacksaws, the 6x4 bandsaws are lighter and have a couple of wheels at the back so can be moved around fairly easily. Mine lives out of the way under the router table when not in use. There is also a lightweight type in the catalog, designed to be clamped on a bench for use, but is light enough to put away in a cupboard. I've not used one, so no idea how well they work.

The 6x4 bandsaws also come with a rudimentary table attachment and while it's awkward, they can be used vertically. I use mine in the vertical position to rough blanks out of steel sheet when starting new loco frames.

Parting off is a series of trade-offs, the deeper the cut, the further the blade has to stick out of the holder, the more the forces try to deflect the top slide. To keep the blade rigid for deeper cuts it has to be wider, which means even more power is needed and it all spirals down on a small lathe until something gives...... I use a 1mm parting off blade in a tee holder for steel, which is mostly when making shouldered screws. I can use a 1.5mm blade in brass, but usually use the 1mm blade up to 1/2" bar and only use the 1.5mm blade when parting off something big like a dome.

Graeme

[Old Man Aaron]

I too prefer the hacksaw to parting off. Good to know it's not just my lack of machining skills to blame - my lathe's only 2" X 12".

[Trevor Thompson]

I too prefer the hacksaw to parting off. Good to know it's not just my lack of machining skills to blame - my lathe's only 2" X 12".

Yes I also feel reassured that it isn't my lack of skill!

[FWLR]

Oh to have room for a toolroom...
You are doing a brilliant job and you will have a feeling of tremendous joy that isn't matched when you finish the loco and getting it running.