The Shop > Metal Stuff

Making Patterns for a Rider Engine

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Country Bubba:
Instead of making a new spindle for the Gingery, borrow a trick from the metal guys and make a spur center that mounts in the chuck. :zap:
Quick easy way to switch back and forth.

Country

vtsteam:
Pekka, yup. But remember, this pattern is also not finished yet, this is just the turned part. For most patterns, fillets and rounding can be added later where needed. I'm not a wood turner....most patterns I make don't even get turned on a lathe.

Country Bubby, yup, many ways to skin a cat. But then I'd have an even longer overhang from the headstock bearing, which on a light lathe like the Gingery is a minus.

I don't need to make another spindle, I just need to bore my present spindle of choice to fit a Morse taper, which would allow not only mounting the spur center I have, but also any other Morse taper center, collet, chuck, or spindle as well.

I'll just bore that out the same way I did the MT on the tailstock.  :dremel:

vtsteam:
Next step is to cut out the 2"x 2" x 3/4" square flange piece. To mark it out, I am not going to draw a square of those dimensions, with a circle in the middle for a hole. Why? That hole needs to fit the turned cylinder pattern,and the square needs to be split, just like the cylinder. Otherwise the whole can't come apart, and it would have to be moulded as a single pattern and coped down.

If I drew out my 2" x 2 piece, and cut it out, and then made the hole, I would then have to split the flange, and it would no longer fit the pattern. You always lose something in a saw cut. If you hollowed out the hole larger (always much harder to do than cut it the right size to start with), the outer 2"x 2" dimensions would also be short on one side.

So what I'm going to do is just make a hole first, just slightly larger than finish size. Then cut the pieces out oversize. Split them. And then put them tight together and draw out the actual 2"x"2 finished size for cutting. That way the pieces will all fit together and yet the outer dimensions will be correct.

Old fashioned outside calipers are VERY handy for checking both the pattern and the diameter of the circle drawn by a pencil compass. Notice I've also kept the circle more than 2" away from an edge -- even though it was tempting to use the planed edge as one of the sides.

vtsteam:
I cut the hole out with my electric hand jigsaw. Unfortunately the curve was just a hair too tight for the blade width I had on hand so the cut was a little uneven. No problem....because I have an oversize piece in it's outer dimensions, I can simply fit the hole better with some sandpaper using the cylinder pattern itself as a sanding block. And, If need be, after sanding both flange pieces to shape, I can trim their split edges further to meet again.

I can do this because I didn't try to trim the outside of the flanges to shape yet. You could make a general principle of this and say, always fit your most difficult shapes in working with wood, and then trim the easier stuff afterwards. It's a mistake to try to draw everything out first, and then cut to that. Or not a mistake necessarily if you're a faultless mechanic. But if you're a regular person, you'll go through a lot more wood and frustration trying to cut to a layout, than laying out in relation to an already completed difficult cut.

If worst comes to worst you can also build areas back up with cardboard or even Bondo (auto body filler). In fact I use both quite a lot when I need a small amount more thickness in some pattern than standard lumber sizes, and also for fillets, etc.

ps. if you have a mill and a boring head that would be a great way to do something like this flange. A hand jigsaw is what I have available, so not ideal but still workable....

vtsteam:
Traditionally the best tool for doing inside curves would be to use a very sharp in-cannel gouge to pare away material. I would say that's probably the best way, too. Unfortunately I just have one out-cannel gouge in this size range. I may convert that one some day, as it's not very useful as-is.

And here, to depart from tradition, I have used dots of hot glue as welding tacks to position the two flange pieces on the cylinder pattern, and then Bondo-ed across the joint face, as well as some grain tear out at a wood flaw in the core print. This will all be sanded back.

I like using hot glue for tacks, as it makes positioning easy while it's still hot and somewhat flexible, yet grabs fast enough to position things without clamps, just holding the pieces in your hand. If you don't quite get it right, just pick off the glue tack and reposition.

I've finally also drawn the cutting lines for the actual flange outline.

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