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Centec2 knee adjustment

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Rainbows26/11/2020 03:43:58
644 forum posts
182 photos

Bonjour

Going to resurrect this thread for a basically identical issue - except the knee casting of my Centec 2 has extra iron between the two webs seen on Sean's machine. Good for rigidity, bad for having a clear space to stick a leadscrew and gearbox and handle and so on in. I'm missing the original handle but otherwise the rack and pinion still functions.

Thinking about working within the limits of the existing set up I don't like that 1) the stop screws aren't graduated 2) if you have to move the knee further than the travel of the screw you have to move the entire stop, thus losing your measurement, 3) if you let go of the lever and the position stop / gib lock isn't tight then the knee will fall down

1) -> replace the screws with micrometer barrels, though I do wonder about the durability of them. Doing repeat cutting passes would get boring fast with no way to switch between precise adjustment and rapid approximate cuts as on a leadscrew dial.

2) -> replace the screws with extra long micrometer barrels? This one I haven't properly worked out yet.

3) -> A mystery to fix. Counterbalancing the knee with a gas spring would help. A switch attached to the handle which actuates a form of lock/clamp would be nice but I can't yet think of a mechanism

If anyone has ideas or has solved this on their own Centec then I'd like to hear them.

Also if anyone has a centec handle for sale I'd be interested, trying to work out that taper and cut a square hole is possible but maybe a bit tedious.

Dave Halford26/11/2020 10:48:44
1142 forum posts
11 photos

There no reason you can't bolt a jack system on the outside of the knee. Finding something with a micrometer dial built in is the hard part. Though a DRO would get you out of that one, then old screw bottle jack would serve.

Some systems I've seen involve the thread going through the base of the mill and whatever it's stood on. A bottle jack avoids that issue.

Peter Howell 126/11/2020 15:07:24
21 forum posts
4 photos

Hi. I'm fairly new to the forum so I missed the original posts. I have a Centec 2 that I aquired several years ago with the aim of restoring.

The knee adustment on mine is by a pinon operating on a rack inside the knee, This is attached to a shaft that passes right through the head stock and terminates in a taper onto which a handle fits. This all looks original.

It would be quite easy to fit a graduated hand wheel in place of the handle. But I do have the much sort after quill feed vertical head.p1000392.jpgp1000389.jpg

p1000391.jpg

Dave Halford26/11/2020 17:44:09
1142 forum posts
11 photos

If you both search for sold centec on ebay you'll see a couple of modded Centec 2's and an amusing price for a Mk3 vertical head thats still for sale can't think why devil

Rainbows27/11/2020 02:43:15
644 forum posts
182 photos

The jack I had thought about using was this:

http://www.screw-jack.com/jtc25-mini-screw-jack.html

https://www.alibaba.com/product-detail/2-5-kN-Cubic-Mini-Screw_60781608045.html

Some measuring showed that it would be just small enough to fit under the knee (vertically speaking) while still giving the full travel. A TR14x4 leadscrew feels like its on the slender side but but the load rating says it could lift the entire mill. For £40 it would as cheap as some second hand jacks. For £100? eh well maybe then homemade is the path to go. Yet to ask for a quote. Unfortunately the 4mm pitch doesn't match up with any mass produced machines so I can't buy a standard spare leadscrew dial to use on my machine so maybe a DRO is the way.

I was thinking that having an off centre leadscrew would be bad for the machine, but then again all our lathes work that way, so maybe I was overestimating that problem and getting stuck in a mental rut.

Something I've seen is stick a big worm wheel on the pinion axle and bolt a mount for a worm gear somewhere on the side. I've been keeping an eye out for scrap rotary tables to steal the gears out of but have yet to stumble across one. Essentially the same idea the Centec company had for the 2A

Optimistic listing there, sure I could buy an entire respectable second hand milling machine for that money but why do that when I can buy a milling head? I still have a milling spindle I bought from china for an eventual vertical conversion, it cost me all of £100 and some change.

Pete.27/11/2020 03:00:46
avatar
321 forum posts
47 photos
Posted by Dave Halford on 26/11/2020 17:44:09:

If you both search for sold centec on ebay you'll see a couple of modded Centec 2's and an amusing price for a Mk3 vertical head thats still for sale can't think why devil

I saw that vertical head, the dealer selling that won an auction I was bidding on to buy lathe (not ebay) he got it for about £1700 with fees, I later saw the same lathe turn up on ebay, which is how I know he bought it, listed now for nearly 3 and a half grand, all his machines are sitting under tarpaulins outside rusting, with ridiculous prices, the guy's straight up delusional.

Dave Halford27/11/2020 11:34:51
1142 forum posts
11 photos
Posted by Pete. on 27/11/2020 03:00:46:
Posted by Dave Halford on 26/11/2020 17:44:09:

If you both search for sold centec on ebay you'll see a couple of modded Centec 2's and an amusing price for a Mk3 vertical head thats still for sale can't think why devil

I saw that vertical head, the dealer selling that won an auction I was bidding on to buy lathe (not ebay) he got it for about £1700 with fees, I later saw the same lathe turn up on ebay, which is how I know he bought it, listed now for nearly 3 and a half grand, all his machines are sitting under tarpaulins outside rusting, with ridiculous prices, the guy's straight up delusional.

As is the "Traction engine body" still unsold on ebay for at least one year if not two.

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