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how would you lathe this part?


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not car related but been using a lathe over lunch in the school i work in (nice and quiet at the moment) and been making parts for my guitar i've built - 3 control knobs and 1 toggle switch.

my question is how to turn the toggle switch. I was going to make it relatively standard shape but without the curves as i'm not a great machinist. It will be similar shape to this




I'll have to do a round hole in the bottom so i was thinking i'd bore the hole first and then cut the angles. The trouble is when i cut it off it will leave a flat and i want it tapered at a slight angle. If i then turn it around to turn that face then the long tapered edges will be hard to hold in the chuck without it sliding out or damaging the aluminium.

The only other thought was to drill the hole smaller than i need and tap it to put a small stud to use to hole it in the chuck.

How would a professional do this?


thanks :)

Oh and car related i put the steering boss in the lathe and took off the flaking paint back to ally. Just finishing a few bits it missed as it isn't perfectly round and debating whether to polish it up and leave it ally

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Looking at the part you wish to produce can be turned on a lathe.

I see that the centre has a rectanglaur hole do you wish to produce this or can you make an insert to fit after machining the shape.

I would start by drilling and shaping the large end with a tool or file the end to shape.

Part off or hacksaw to length.

Fit on a mandrel held in the chuck and shape the part to a taper, with the use of the compound slide, file the end round if required to your liking.

Polish to your liking with very fine grit paper.

Hope this gives you an idea on how to start.


Edited by maca
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cool thanks for that makes sense.

I'm just going to have a round hole instead of the rectangular one as it'll be so much easier. because everything is metal i can just put a dob of glue stick on the end of the switch and heat everything with a soldering iron to get it on and off. (hopefully)

really useful to learn about mandrels as didn't know that before. Think that will come in useful. Also wasn't really sure it using files etc was the done thing but watched a few videos last night so will give it a go.

fingers crossed :)




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I am sure you must watch Ben Crowe at Crimson?  I have been so tempted to go on one of his courses but by the time you factor in the course costs, accommodation for a week or more and materials, it is just too expensive.  I also have too many guitars already! :) 

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1 hour ago, David S said:

I am sure you must watch Ben Crowe at Crimson?  I have been so tempted to go on one of his courses but by the time you factor in the course costs, accommodation for a week or more and materials, it is just too expensive.  I also have too many guitars already! :) 

No David sorry to say never heard of Ben Crowe!

I worked in a machine shop for many years and worked on most machines in my time so time served machinist.



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thanks. yeah a vid i watched said not to ever put your hand over the chuck and also not to have a sharp tang on the file (put a handle or something on it) in case it catches and comes back at you.

Being a newbie I'm being over caution and taking my time which means my guitar parts which you could probably knock out in <30mins are taking me hours and hours :) 

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Also be aware it is illegal in the UK to use emery cloth or a file or any hand held cutting or polishing media in a lathe unless held in a jig. I did not know this until last year when a work mate had a finger skinned when his emery cloth snagged and pulled him into the work piece. He was a machinist with decades of experience but sometimes it happens to the best operators. 

As a result of his injury we had the heath and safety executive come on site and crawl all over the place. We had meetings telling us how it’s now outlawed etc etc. The company got a £1.6M fine from HSE because of the incident and for not having records of educating employees against the practice. So don’t end up in his position, stay out of trouble and more importantly don't hurt your self. 

At home you can still do it, but not in a work place. HSE have no jurisdiction over private homes and private individuals. 

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Thanks Barry,

Good point to bring to our attention with regards to health and safety and the use of machinary.

I now have my own lathe and milling machine in the garage so would not come under HSE.

Reading Ryan's post

I assume he has permission to use the lathe at the school and has been informed of all health and saftey matters.

Regards Martin

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Not trying to be an arse by the way, just pointing it out. The rather large fine we received was enough to make the company twitch. But as you say working at home is nothing to do with HSE. 

I would still happily use emery and a file in a lathe because I always have done. Not at work tho it would be instant dismissal if I got caught after recent events! 

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cool, always happy to recieve advice on health and safety. I'd rather be aware of it. I've not really been given much of a guidance on the machines to be honest. I'm just careful about what i do as i know the machine is just looking for a reason to get me!

A few things i do to minimise risk. I take small cuts, turn the chuck by hand before turning on to check nothing is going to bind, check where the tool is going to finish and that the holder etc isn't going to crash into the chuck, keep my hand on the lever for autofeed.

I did use a bit of emery the other day but i have a block of rubber i use as a sanding block which is underneith it so if it got pulled it it would just slip out of my hand.

You say it needs to held in a jig? how would this work for rounding corners etc. Is this one of those health and safety things that isn't actually practical in use?

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I don’t work in the machine shop I only do foreigners on occasion. I did about 18 months turning as a teenager tho and emery cloth by hand was common for taking a tiny bit off a diameter or even adding a thou touch a diameter oddly enough.
As always no lose clothing, no long hair, no gloves, no necklaces or dangly stuff, no no and no. And NEVER leave the chuck key in the chuck!!!

As for creating a radius, use a radius tool. If you don’t have one you grind one. That’s the correct way. We have all used a file tho. 

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  • 2 weeks later...

well i got it done (was also doing 3 knobs which took some time). I'm quite pleased with the results. Was a fun little project and learnt a few bits. Thanks for the heads up about using a mandrel. I cut a piece for it to sit on when i turned it around to do the final angle cut on the end. Gotta make another one for my other guitar now :)





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