Lathe spider

[Alpha1]

I have decided to machine a new barrel spider.
I all ready have a spider fitted to the lathe:
But: My main metal working lathe is a hobby lathe so limited in size and what I can do with it. When I first got it I thought its big enough for my needs I wont want any thing bigger for the projects I am going to build.
Wrong: So very very wrong.
Any way the first spider was a learning curve I approached a machinist at work (I have mentioned him before) so I we made a spider I told him what I wanted and made a sketch. Eventually the spider got made and was fitted to the lathe. Great: Except the guy as good as he was/is had only ever worked on industrial machines.
Any way I watched a couple of you tube videos and it occurred to me that my lathe spindle has a M27x1.5 thread on the back end of it that I could of screwed a spider onto.
So thats what I am going to do.
I am going to make a new spider with a M27x1.5 thread and screw it onto the spindle:
Just so you know I am not making it up. I will post pictures I am waiting for a chunk of aluminium to arrive once its here I will up date you. Cutting an internal M27x1.5 thread should be interesting. Any one know what diameter I should bore the through hole to to accept the M27x1.5 thread.

[Mattnall]

According to one source I have 25.5mm should do it.

tap-size-chart

[ovenpaa]

Also, the threading/screwcutting is the first stage. Once the thread is cut and the blank screwed to the machine leave it in place for everything else to keep it all concentric. This just leaves the screw holes which can be done on the mill. Make sure the part fits in your vice!

I did similar with a D1-3 backplate on my Chipmaster. Not only did I not remove the part from the machine for the duration of the machining, I also marked which stud aligns with the back plate so it is always as close to concentric as that set-up can be when re-fitted. Not that is matters as you clock in the part afterwards. Right, now to my view of the spiders; they are very limited in application and my one is mostly used for bolt work, so opening the bolt face and accurising. The rear spider is used far more than the front one. Yes, they look good on the shelf and people always marvel at the D1-3 I machined, however things like my hand vice or ebony wedges are used dozens of times more a year than a spider.

Just one thing, beware the flywheel effect of a large spider with a barrelled action or whatever in it that is braked/stopped suddenly. This is why I would never entertain a screw on chuck system..... :)

I just asked Christel what she thinks I use a lot of and she promptly replied a micrometer, screwdrivers/turns screws and the angled wrench for swapping tool holders on the lathes, oh and needle files, I have lots of them and use them all the time. Interesting eh?

[Andy]

25.5 would be ok if you were tapping it but as you are screw cutting you need to go a bit smaller.
25.376 is bottom size so I'd go with 25.4.

[1066]

As it's a spider and you will clock part individually I guess it's not so important but for something like a back plate I think a slightly slack thread so it could be pulled up to a square shoulder or register would work. Being another self taught hobby scratcher I mostly make it up as I go - The only golden rule is to double double check before you bore your hole, I have a few paperweight in the workshop to prove my point.

[Alpha1]

Well thats another paper weight I bored it out to 25.5 the thread is far to slack. I will have another go and see how I get on.

[Alpha1]

25.5 would be ok if you were tapping it but as you are screw cutting you need to go a bit smaller.
25.376 is bottom size so I'd go with 25.4.

Good advice I should of acted on it. I will have another go using a smaller bore size.

[Andy]

25.5 would be ok if you were tapping it but as you are screw cutting you need to go a bit smaller.
25.376 is bottom size so I'd go with 25.4.

Good advice I should of acted on it. I will have another go using a smaller bore size.

I'm a time served turner Dave. Any questions just ask. I'm not sure you know but I'm also in the same club as you.

[Alpha1]

You must be in TVTS then. What are you shooting? I run the Tuesday night underlever and organise the MOD bookings.

[Alpha1]

I have had three attempts at this now and each one was a total failure. It says in the manual that this thread is 27x1.5 I am convinced it is not. It's a Chinese lathe so I should have known better.
I think it's 27x1.0 mm I will check tomorrow with a thread gauge. Yes I know I should have done that in the first place. Hindsight is a wonderful thing.