Centec 2B - New arrival and Q&A

Mine won't either, the lead screw needs to stick out of the mounting plate a few thou further.

I figured it out - the knurled wheel is threaded onto the cylindrical arbor inside and it was rusted solid on my X-axis dial. I used some loctite to bond the whole assembly to a mandrel and then was able to break it free after soaking in WD40. After reassembly I put the wrong spacer on the wrong dial - which meant no matter how much the wheel was unscrewed it never locked tight. After swapping them back over, both are working as expected.

There is an additional washer between the knurled ring and the handle on the Y-axis to make up for it being a smaller casting - are you missing that, Dave?

On my VH the nut screws onto a pin which is inserted from inside the VH, so don't push it in unless you want to dismantle it. It's not connected to anything inside and doesn't act as a stop for the quill. I used it as a convenient method of attaching an external stop block when I made an adjustable quill stop.

You may well be right, I just tried an extra washer under the acorn nut and it now works. The woodruff key has a nick taken out of it so it is able to go into the arbor so something has been fudged.

Edited By Dave Halford on 30/07/2021 16:14:22

Thanks Gary! Mystery solved!

I've found a fair few things loose on the mill in addition to the siezed knurling ring, the handwheel bosses, almost all of the gib screws, etc. but tightening them up has certainly helped.

I was wondering why the half-nut kept disengaging on the X-axis, and it was a combination of the handwheel boss being very loose and allowing the rod to jiggle around enough to disengage, but also that the half-nut locking mechanism has been modified.

The original arrangement was a nut that clamps the half-nut engaged or disengaged, it's movement actuated by a short hand lever as shown below:

One of the previous owners of this mill has modified this, with a long arm that reaches underneath the table toward the operator, with a rest bolted onto the hole marked '15' in the above diagram. If the arm is in the rest, then the half nut is pulled upward and engaged. If the arm is moved off the rest and let fall slack, then the half-nut is disengaged.

Maybe this solution worked when the mill was new(er), but as it stands the half-nut kept flopping open. I hope that tightening up the bosses on the end of the table has helped, if not I might need to find a way to reverse engineer it!

Edited By William Ayerst on 31/07/2021 11:37:48

The half-nut may be worn so that small side pressure pops it open. I notice that you still have the rapid return spider, so you probably want to use the half-nut properly. I removed mine and keep the half-nut permanently closed.

A slight mod I made to my Centec was to the Y-axis gib-locking screw. It's a long Imperial threaded socket head screw which I found tedious to use. The Allen key kept falling out and I didn't have the wherewith all to make a custom version, so I made an extension from a piece of aluminium that's a press-fit into the socket head.

It works for me and encourages me to lock the Y-axis more often.

My machine doesn't have half nuts. It’s been converted to a solid feed nut. The y axis locking screw is a longish flanged-head hex bolt, on which a combination ring spanner hangs (almost permanently). The long travel is limited by when the power feed motor contacts that bolt. If I wanted a bit more x travel I could replace it with a shorter bolt and use a long-form socket on the head (but I await the need to do that).🙂

The x and z locking screws are of a similar arrangement. They, too, each have a small combination ring spanner hanging on them.

I'm not sure I have a need for the rapid return capstan handle, certainly not for the scale of model engineering work I'm currently doing!

This is a picture of the assembly showing the original handle and pivot, a pinned steel plate (I gather the two pins are the centres of the elongated slot that would take the nut) and the brass handle:

After tightening up the bosses on both sides it seems more reliable and hasn't popped out since, so for now I'll leave be - but I think all things considered I'd prefer a more long winded process to disengage the nut but which is more secure when it's engaged.

Any ideas on how I might reverse engineer it, should this be required?

Thanks for the tips on the locking nut handles - not a bad idea at all. Do you know what thread the halfnut locking bolt will be, or what the gib locking screws are?

All the best and thank you again, both!

Edited By William Ayerst on 31/07/2021 21:22:53

The half nut thing on mine is a bronze casting. On the left (using orientation of your photo) is a curved slot with a bolt to clamp it in place. It looks as tho' yours has been modified, but can I see it peeping out underneath?

I took the quick traverse mechanism off mine, it got in the way, and having adjusted the half nut right dropping it in and out didn't seem all that good an idea. It's not like a lathe, no in/out stops.

Edited By duncan webster on 31/07/2021 22:28:21

Yeah, I think those pins visible through the black steel are the extremities of the slot.

Is removing the quick traverse a reversible operation? I'm not using it right now but I'd not want to make any permanent changes just yet!

So come on William on a scale of 1-10 how chuffed are you with you new stallion..

Steve.

Very reversible, you need a long box spanner to get at one of the nuts, cant remember what size, Whitworth and not that big

Dear Steve, I'm over the moon - I put together a video about it:

https://www.youtube.com/watch?v=8dm0KNm7mJU&t=38s

Regarding the half-nut situation, I'll see if I can get the plate off the bronze casting and those pins out without risking damage tomorrow and see what's going on.

Did you remember to snug up the damper ring on the Clarkson to the underside of the quill.

Steve.

Hi Steve, the Damper ring is on there pretty tightly. Is there a certain spanner I need to get it unstuck? I understand it's a left handed thread but it's on there tight in either direction!

The gib locking screws are 1/4 BSF

Yes the eject/snugging ring is on a left hand thread, so a short length of bar in one of the holes, and a sharp tap with a hammer, should release it OK; mine was jammed when I got it too. (tie a bit of string to the bar before how hit it. so you can find it again)

Next purchase is a bottle of port; when consumed, use the cork to block the end of the horizontal taper to keep the swarf out; they are a pain to clean, since they have the captive drawbar.

Bill

This is the 2A half nut, the 2B is different I know as is the travel stop bar (I think mines been moved)

Your stop bar looks non original

I managed to get the modified half-nut handle off and luckily, no permanent modification - the screws and pins just pop out. I need to figure out what thread the locking nut is, though - I have a piece of 3/8" BSW and it seemed to fit but locked up after a turn or so, so I'm going to assume it's 3/8" BSF?

Dave, I don't suppose you'd be able to check for me by any chance?

I've been switching between horizontal and vertical milling and having alot of fun - I must admit though, I almost s**t my pants when the horizontal arbor locking nut caught on the support and started unscrewing, cranking the whole horizontal arm out at the same time! 

Edited By William Ayerst on 01/08/2021 16:22:13

"What is the purpose of the nut on the front of the vertical head? It seems to just spin in place on my one."

It limits the vertical movement of the quill, otherwise it would hit the oil level dipstick which does.

2BA grub screws for the gib adjustment on the 2A, as above 1/4 BSF thread for the locks. All the threads on my 2A are either BA or BSF, I assume they would not change for the 2B.