Thread: Hi, and a "how would I make this?!"

New member here - I'm a 'relatively okay' amateur metalworker. I get along okay with a lathe and mill as long as it's not too complicated but it's all self taught so by no means that advanced and haven't got a clue on most of the correct terminology!

That said, I need to make something and I don't even know where to start let alone which tools to use.

On a project I'm working on, there is a partially splined shaft that currently has a lever on, but it's 180 deg out of where I need it to be. The shaft cross section looks roughly like this:

Untitled-1.jpg

The lever that's on there can't be reworked for the purpose, it's cast iron, it's damaged and it's a bit crap.

The 'troughs' of the splines in the shaft are radiused and below the general level of the shaft surface, the 'peaks' are above the general level of the surface and square-ish edged.

Any clues on how I'd machine out the female version, or is that a 'you need special tooling and have no hope' type job?

Welcome to the forum
I think you are getting close to the 'need special tooling' option but there may be things that can be done. So if I understand you correctly, you need to make a hole with that profile?
Some dimensions would help to start with. What is the diameter of the hole and how long is it?
What it is for would help too. Does it have to slide up and down the shaft? Is it an occasional use thing? Does it have to transfer much force? Is the function critical? Does any repair have to be 'like the original'? (The reason for the last is I'm wondering whether the simplest way is to drill a hole in the replacement, provide clearance near the spline and then after coating the shaft with mould release, pack the cleared area with metal putty or similar).

Michael

Hi Davince,

Welcome to the forum.
The hobbyist method of cutting splines in a bore would require something like a slotter and a cutter with the correct shaped tool. The work piece would need to be held such that it can be rotated so that each spline can be cut at the correct angular position. Commercially it would be done with a pre-shaped broach and the broach would be pressed though the bore to form the spline shape.
Without more information it is difficult to offer more than general advice.

Looks tricky.
As an alternative solution, can you do a scotch key?
It's easy and effective.

Jordan

Hi Davince

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Again, welcome to our group.

Grahame

You said the original lever can't be reworked, but could you cut the handle off the lever's hub and turn the hub down to a sleeve? Then you would have a cast iron sleeve with the correctly shaped bore to fit the shaft. You could then fit a new lever to the sleeve.

A photo would be a big help.

Thank you for all your replies, very much appreciated! Yes Machtool is correct, I'm in the UK - this is about the only engineering forum I found that had people speaking in terms I could understand lol.

To cover the queries raised...

Yes, I need to make a hole in a piece of steel that shape. The shaft it sits on as per the image is 20mm diameter and 16mm long between the bush it pivots on and the circlip that retains the lever, so this shape needs to be broached (new term learnt, thank you!) through a boss 16mm.

what it's for... it's a clutch throw out actuation lever on a 1973 VW beetle gearbox. It's no longer in a beetle though and is being converted to hydraulic from cable operated. Originally a 'pull' setup, it now needs to be a 'push' setup and there isn't room behind the lever to mount anything, and there isn't enough room under the new covering to have the lever where it was, hence needing to rotate it 180 deg.

I did consider machining down the existing lever to just be an insert in the new lever, but it takes quite a lot of force to shift and was concerned how I would then mount the cast iron into the recess without it becoming weak and failing.

I'll do a photo soon as I'm back out in the workshop as well but hopefully the above will help.

I could in theory convert it to a scotch key but it would be a tad painful to say the least, and I'm trying to keep as much of the mechanics that could fail original - if I need to change the 'box out, I'd rather not have to strip a replacement to change the shaft each time (I say this because the 'box is the weak link in the setup so am anticipating having to do that!)

Originally Posted by Davince

I did consider machining down the existing lever to just be an insert in the new lever, but it takes quite a lot of force to shift and was concerned how I would then mount the cast iron into the recess without it becoming weak and failing.

Welcome back!

Roughly how much "meat" would be left on the insert after machining it down? I.e. What would be the wall thickness of the insert?

One way that should be more than strong enough, is to cut the lever off, leaving just enough to turn into a cylinder. With the new lever, machine the bore to suit the cylinder, once you have the location correct, making it a press fit, then drill a hole in the join line and thread this with a 5 mm tap, then insert a 5 mm grub screw with some loctite so it won't come loose. I think they call it a scotch lock, it's the same principle as a keyway on a shaft and pulley, and that idea has been around for a long time.
Kryn

Davince,
As the original part is from a VW it would more than likley be a forged part not a cast iron one. Can you check it as it would be a lot easier to cut and weld a new lever arm onto the existing part if it were a forged one.
Bob

Originally Posted by Davince

The shaft cross section looks roughly like this:

Untitled-1.jpg
The shaft it sits on as per the image is 20mm diameter and 16mm long between the bush it pivots on and the circlip that retains the lever, so this shape needs to be broached (new term learnt, thank you!) through a boss 16mm.

Thanks for that detail. Occasionally we have someone show up and the drawing is not to scale which makes things totally misleading.
At that size and length, I would suggest that the best bet is some one with a shaper. Grind a tool to produce that form and cut it like they would a keyway. A method of rotating the part so that the 6 notches can be cut and I think you would almost be there.

Michael

That job should be reasonably straight forward with a rotary table and milling machine with a bit of hand work.

Its probably easiest to draw it up in CAD to get your bore diameters. Blue up the material and layout your diameters, from your drawing it looks like you will have 3 different diameters; the smallest will be where the slides land, the mid size is the main shaft body, and the largest diameter will be the peaks of the spline. For the splines it's probably easiest to print out a template and use that to copy the spline shape to the blued part by scribing around the template. You could of course work out the actual geometry in CAD in lay it out with a compass, but normally these types of things have a fair amount of wriggle room. How much effort you go to here will depend on the desired accuracy.

To make it, Drill/bore the smallest diameter, that will rough out most of the material. Locate the bore on the rotab and machine the middle diameter (ie the shaft) bore. With a bore that size it's likely you may need to clean up the ends, just depending on how small an endmill you're happy to use. Finally use small hand files to finish up the splines. I think many people these days don't give enough credit to bench work, yet with care it's possible to file to a scribed line and be within a few tenths of a millimetre. You may even be able to rough some more material with a small end mill and the rotary table. If you have the male shaft it will be easier as you can find the fit as you're filing.

Obviously the above is completely impractical for anything more than a one-off, but I think it would be entirely practical for your application and wouldn't take as long as some may think, certainly less time than making special tools etc. Many people don't even blue and layout work these days (I'm one of them!), as such it's becoming somewhat a lost part of this field. Yet I'll still often do it and it's saved my bacon on numerous occasions, where I would have machined away and scrapped a part as a result of a moment's brain-fart.

Good luck with it and hope you show the end result.

I am with Pete F too, it can be done if you have dividing-head or rotary-table as another option
Or lasercut if you can send the file to someone?

Might be a bit small for that guys although it is possible I suppose
I've scaled the profile and the arcs between the prongs are R0.8mm. Through 16mm thick steel could be a bit of an ask, especially with laser and it's kerf.

I tried working out the spacing between the prongs but there is not a nice round number that does it

If going CNC, I'd suggest wire cut.

Michael

With obvious due respect I think you're approaching this as an engineer and possibly overthinking it Michael. With respect to the intended use, there isn't a whole lot of precision required here and a perfect fit won't achieve anything that an approximate fit won't similarly achieve. If the spacing between the "prongs" is 0.8 mm then the job becomes even easier and you run a hacksaw down each one then, as stated above, clean up the remaining material with a file.

The precision comes from the fit on the shaft, and a 5 mm end mill on a rotary table can be spun fast enough on most milling machines to run around a 16-20 mm bore on a rotary table to create that profile. Obviously stepped down in suitable sized cuts. The splines/prongs are merely to stop rotation and even if completely bodged, if filed to fit the worst that can be expected is they don't wear well. But in 16 mm steel for the stated use I don't think that will be an issue. Filed with care, they would be more than suitable.

Clearly this could be wire cut or water jetted, but I suspect the OP probably doesn't want to go to that (considerable) expense and is looking for a way to achieve a result with only minimal resources.