Half a job looking good so far (and any ideas?)

I’m getting more into Fusion 360, and more comfortable with 3D modelling, so I thought I would try out a more complicated 3D carve (since so far I have been doing essentially 2D).

I decided to try carving a shift knob - not the most complicated shape, but something I could improve on and try some prototypes out of scrap wood before using better stock.

The results at the half way point look pretty good. Here is the roughed stock (using Fusion 360 3D adaptive and a 1/4 inch downcut endmill):

And here is the progress and result of using radial finishing passes:

So I’m loving the results so far - but now it’s time to cut the other side.

I have some ideas for work holding and centering - mainly to bore a locating hole in the top, and a locating hole in a fixture plate, and thread them both (being sure that both are bored to a known XY zero).

Any thoughts for making sure it well secured? The last thing I need is for it to unscrew itself while it’s running. I thought about milling flats onto the base, but that seems like it would ruin the look. I think I would like to make a few of these - so solving repeatable work holding would be a handy thing.

2 Likes

Very nice. Following as I want to make one also.

Right now I am working on a tray to hold billiard balls. Could you give a bit more detail on the tool paths you used? I have the tray modelled but cannot figure out tool paths.

As for work holding, maybe leave a square projection on the base ~ 1 cm thick. With a centering pin for position you could then clamp the square projection. Then saw it off when the top is done.

What is the overall height of the stock?

Thank you @Ryecon - keep us informed of your billiard tray, I’m sure we would all love to see it.

For the toolpaths used, first pass was 3D adaptive clearing with a 1/4 inch down cut endmill, with a cutting feedrate of 80 inches per minute, plunge at 20 inches per minute. “Optimal load” was 0.1 inches (I believe that is how much of the cutter gets engaged in the work). Stock to leave of 0.02 inches radially, and 0 axially.

Second pass was Radial, selecting the center point to be the center of the knob’s base. Same tool and feed rates, no stock to leave.

To cut the two sides of the knob, the stock is modelled in two pieces, with the dividing line being the widest point of the knob (so that the cutter can reach both sides).

The overall stock height is 3 inches - which leaves just under 1/5 inch to drill a hole in the bottom as pictured and use it as an alignment / hold down for the first setup.

Here is the 3D adaptive clearing pass:

Pictured below is the setup for the radial pass:

For machining the other side, I have a second setup with the part oriented the other way around, and a repeat of the same two operations. If that goes well, I will see about carving a logo or shift pattern in the top of the knob when it’s done (without removing it from the machine, so that I don’t lose my zero).

I have also toyed with the idea of cutting a “nest” to cradle the part out of scrap, for work holding if I want to put the part back in the machine accurately for any further cutting. Fusion would make it easy using the cut operation.

@elbarsal Looking very fine, Ed. In terms of holding it down for the other side, I think that @Ryecon/ Andrew’s idea is a good one. If it’s too late in this project to do that, I suggest that you use a waste block. Wood turners frequently use waste blocks to hold their bowls, etc. They are nothing more than a block of wood that will be “wasted” when the project is done. The bowl can be attached to the waste block with glue, double sided tape, mechanical fasteners, etc. The waste block is held onto the lathe and when the bowl is finished, it is removed/cut off.

You could attach the knob to a waste block, then hold the waste block down to the spoil board with clamps, tape, etc. If you choose to hold the knob to the waste block with a screw up through the centre of the knob, be sure to set the CAM software to carve in the direction that tightens the screw. :grinning:

Thanks Grant!

Yeah I am thinking of something like you say, screwing up into the knob to hold it. I think Fusion even defaults to clockwise (tightening) adaptive clearing. I might have to remove my spoil board to get a bit of height back to do so, since my machine isn’t up on feet (which puts the top of the stock at 3.75 inches above the bed of the machine).

I will post my progress - I’d like to get this one finished, even the prototype looks so good so far! My only real quirk now is the car the final knob is going on (Triumph Spitfire) takes a 5/16 UNF thread, and all the inserts I find are 5/16 UNC - but that can be dealt with - maybe with epoxy reinforcing and just tapping it directly.

@elbarsal In my previous life, I rallied spitfires, mgbs, mgas, even mini coopers - in short anything that I could get my hands on. I think that you will find that if you tap the wood directly, you will be fine. FWIW, when I tap wood, I run the tap, then flood the threads with thin CA. Let it dry thoroughly without accelerator, then run the tap again. You will end up with very hard threads.

Please post the final product, Ed.

1 Like

So the scrap wood I am experimenting with didn’t take a thread really well, and secured to a waste block, it exceeded the available Z space for my current setup. Things were pretty precarious, too - so I decided to try milling a “nest” both to get some Z back, and to better secure the work.

Getting Fusion to generate the internal finishing pass was a pain (for @Ryecon I had to use “Contour”), but when I finally did, it really fit like a glove - pretty well press-fit. Between the nest and the so-so threading (I threaded it down into my waste board), it was surprisingly stable, and I gave it a shot.

I think the results speak for themselves - I’m surprised at how nicely the top and bottom cuts mate (a key is that I cut the nest to the same XYZ zero as the final cuts on the knob.

Adaptive clearing was a lot of fun to watch:

After adaptive clearing:

And the final result:

The discontinuity you can see can’t be felt - it really is that smooth. With some light sanding, I think it will really come out nicely.

I think with some reinforcing CA glue like @gwilki is suggesting, even my prototype can be turned into something usable.

Now to etch / engrave a logo or shift pattern onto the top!

1 Like

Quick update - Triumph logo carved in… and a small dent from a bone-headed crash setting my Z zero. That’s why this is a prototype / made from scrap.

The close up shows the lettering well, but also the fact that this is softwood of unknown origin - still came out nicely though, especially after a light sanding. Going to hit it with some finish and see if I can get it to shine.

3 Likes

I have had two TR3’s, one TR4, one TR4a, one Spitfire, and one TR6, the beast! Must have been a glutten for punishment, they could sit in the garage and just break on their own!

@Bill there really is nothing quite like an old British roadster!