Centec 2A Drawbar

I need to make the drawbar eject for a centec 2A mill (mine is missing). I came across this picture on a previous thread and it all makes sense, except, what is the spring for ?

https://www.model-engineer.co.uk/sites/7/images/member_albums/94472/823008.jpg

They never had one to start with Andrew.

Thanks, that explains my confusion. I should probably dig out some exploded parts diagrams.

The drawbar is just the long piece above the ruler. The spring sits on top of the quill and is not part of the drawbar at all, it is held in place by the circular nut. The nut is removed by the spanner, which is only required if you need to remove the quill for some reason.

That one's my photo, and is the drawbar and cap from a Mk3 vertical head, on my 2B, to help return to the quill to the top of the vertical position.
As it happens, I've just made two new ones, one 3/8" BSW and the other M10, so whilst you're geared up, it might be an idea to make a matching pair.
My older milling/drilling chucks are all imperial, whereas new replacements are normally cheaper if you buy M10 ones.
My horizontal draw bar doesn't have a spring.

My clamping kit, T bolts etc, are all M8 with 17mm flange nuts, so I also made a peg socket with a 17mm hex head to facilitate swapping draw bars, rather than struggling with the peg spanner shown in the photo.

Bill

A typo maybe Gary, you need to remove the circular nut to change the vertical drawbar, rather than just to remove the quill.

Bill

Ah ha, pushing the quill back up makes sense. I'd never really thought about the quill not returning as I normally use the rotary handle to wind it up and down then lock it off when not in use. I'll factor that into the design, looks like it'll want a bit of space for the squashed spring on full quill extension.

Hello Buxton by the way, I'm just a mile or two over in Wormhill.

If you want to pop over and measure anything, you're most welcome.
We have a working kettle too.
North west side of town Hogshaw/Lightwood area

Bill

Edited By peak4 on 01/08/2022 14:24:42

Thanks, I might take you up on that. I'll blunder on for now and see how far I get.

Will M10 go through the mandrel? Previous posts on here have said it won't

I've only tried it in my Mk3 vertical head, but yes it fits fine.

Bill

You're welcome anyway if you're in town.

Just drop me a PM first, as although I'm retired, I'm still out quite a bit with the camera.

Bill

On my vertical head M10 threaded bar will drop through the spindle but it doesn't take much runout in a piece of 10mm rod to bind up. I've opted for 9.5mm final dimension on the bar with a short threaded M10 section (20mm) to engage with the taper threads.

I'll post a picture and prints when I'm done. First attempt in the scrap bin after trying to press fit a collar that was a bit more interference than I expected and noodled the rod. Second attempt just turning out of solid bar, you live and learn.

No typo. On my MK3 VH the drawbar is not retained in any way. After unscrewing it from the tool-holder/chuck whatever, it is free to be removed. I suspect that my VH isn't standard because its ISO30. With ISO30 a gentle tap is all that's required to free the tool from the taper - there is no need to forcibly eject the drawbar.

I have a Mk3 VH and 2Mt spindle, 10mm threaded rod drops straight in with a couple of nots and a washer . I have a clarkson style collet holder with 5/16" BSF so just cut the 10mm down and rethreaded. Not tried 10mm in the 2MT horizontal spindle - yet. A job for today ! Noel.

That's good to know, saves the hunt for 3/8 BSW tooling.

NO ! 10mm will NOT go through the horizontal spindle, it enters about 8" from the pulley end ! BUT bearing in mind the fact that a drawbar is only to stop things falling off AND 3/8" is 9.5mm I would try just skiming the 10mm down a touch and see IF it will hold. Plus for imperial just run a 3/8" die down ! PLAN B, use 3/8 UNC threaded rod, it will be near enough ! Noel.

I wonder if that is because the drawbar is permanently fitted to a rotating spindle, spinning even when the vertical head is in use.
A 3/8" drawbar in a 10mm hole would probably rattle too much.
If there is a need for a 10mm horizontal drawbar to accommodate specific tooling, I wonder if an option might be to ream out the spindle and make a pair of drawbars with a 10mm shank, but 10mm & 3/8" ends.
Alternatively for a one off job, feed in a 3/8" drawbar from the front, but with a wider 10mm front end, and use a couple of 3/8" locknuts on the rear.

Bill

Just a quick update on the M10 horizontal topic.
Like Noel, my newly made M10 vertical drawbar is just too big a diameter to fit in the horizontal spindle.
It's pretty immaterial anyway as, in my case on MT2 spindles, the vertical drawbar is longer than the horizontal one.
However a length of M10 commercial BZP threaded bar, being slightly undersize, is a nice snug fit and perfectly usable with M10 threaded arbors.

Bill

Peak 4 is right ! This evening I tried again with a length of ordinary m10 treaded rod, it is a perfect fit ! The bit I used yesterday had a slight bend that caused it to go tight. I have a length of 3/8"unc on it's way for imperial holders or shafts. Why make/ machine a drawbar when threaded rod will be fine and should not be done up too tight anyway ? Noel.