Creating a spiral

[Chris Cooper 5Participant @chriscooper5]

Anyone got the first idea as to how I go about creating this spiral?? Cheers

[HopperParticipant @hopper]

I’ve done similar by marking it out and filing it to shape, after first making a hacksaw or Dremel cut for the driving face of the dog. Use a piece of emery tape wrapped around the job to mark out the spiral part. Then hacksaw or Dremel the slot to full depth. Then file with a 10 inch flat file. If they are just those common locking levers etc, spiral does not have to be any kind of perfect.

Same technique used to make special counter boring tools and the like from silver steel. It’s not hard.

You could mill it but its a lot of faff, requiring a dividing head geared to the longitudinal movement of the milling table and a second set-up to mill the sharp corner at the base of the driving dog face. Not worth the hassle for such an application.

 

 

[Tony Pratt 1Participant @tonypratt1]

Hopper is about right with his reply and I’m thinking the original was cast.

Tony

[Speedy Builder5Participant @speedybuilder5]

isn’t it a job for the rotary table / dividing head which is set at the angle of the slope?  A bit of careful milling as the face of the slope is perpendicular to tilted axis. This is one I made for the start dog of a vintage car.

[HopperParticipant @hopper]

Yes machining it as one flat face like that is much simpler than dividing head geared to the table travel. It won’t be a true helix, but neither is the filed version so it will work just fine for this application. Looks like a nice job there too.

[bernard towersParticipant @bernardtowers37738]

In a lathe with toolpost milling attachment and lathe in threadcutting mode, turn lathe mandrel by hand.

[Les Jones 1Participant @lesjones1]

You could a setup like this that I used to cut a helix.

 

The right angle drive was for a drill.  You just need to work out the gearing to get the correct pitch helix.

I also used this type of setup to make this drive dog.

To get a sharp corner you would need to use a small diameter end mill and undercut the end slightly of finish the radiused corner with a file.

Les.

 

[bernard towers]

On bernard towers Said:

…lathe in threadcutting mode…

A modern take on the threadcutting aspect, especially if it would be difficult to set the lathe up for the coarse pitch the object requires, would be to 3D print a facsimile of the object and use it as a copy template (like how rifle stocks were duplicated from a hand-made master pattern).

The helix cutting above reminds me of a woodworking contraption, I think called a router lathe, that used a tensioned steel cable over different size pulleys to synchronise rotary and sliding movements. I guess in that situation, some potential slip would not be a disaster, unlike in threadcutting.

[JasonBModerator @jasonb]

If you are going to 3D print then why bother with the lathe just 3D print it in plastic like the original or get the part 3D printed in metal.

We have all assumed that “create” was the physical making but maybe Chris wants to know how to create the spirals in CAD?

If it is the physical cutting then holding the work horizontally in a rotary table and doing a series of plunge cuts to calculated offsets will also produce a spiral, faccet size just depends on what increments you choose to use. You can get quite good spirals that way, a bit of needle file fettling to finish.

 

[noel shelleyParticipant @noelshelley55608]

I had one made at work ! It was a 3 spiral for an Austin Champ, it was milled, 3 sloping faces – worked fine . Noel.

[Phil PParticipant @philp]

I made a clutch release dog with three lobes for a model barring engine.

I used a slotting head and geared the dividing head to the table traverse on my milling machine.

[Phil P]

On Phil P Said:

I used a slotting head and geared the dividing head to the table traverse on my milling machine.

If you could accept a bit of filing, you could do the same but with mathematical gearing instead of mechanical gearing between leadscrew and dividing head.

Work out the table advance per degree of revolution and proceed from there.

One degree of revolution is 360 divisions, so you could do the inverse – work out how many divisions of the full circle would result from 0.005″ linear steps of movement and pick a plate and hole circle to suit.

[Chris Cooper 5Participant @chriscooper5]

I should have mentioned that its the one on the left of the pic I want. I can get them 3D printed, but I was just curious to see if I could make one.

I don’t have a lot of the gear mentioned in the answers.

It is just a camera tripod locking lever so probably doesn’t have to be exact.

[JasonBModerator @jasonb]

For that sort of use a hacksaw and file should get you close enough

 

Two sideways saw cuts half way through it at opposite angles and then a final cut to do the vertical face. Bit of file work to smooth the transitions.

[Author]

Posts