Centec 2B – New arrival and Q&A

[William AyerstParticipant @williamayerst55662]

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

[Gary WoodingParticipant @garywooding25363]

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.

[not done it yetParticipant @notdoneityet]

Posted by Gary Wooding on 31/07/2021 16:39:33:

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.

[William AyerstParticipant @williamayerst55662]

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

[duncan webster 1Participant @duncanwebster1]

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

[William AyerstParticipant @williamayerst55662]

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!

[SteviegtrParticipant @steviegtr]

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

Steve.

[duncan webster 1Participant @duncanwebster1]

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

[William AyerstParticipant @williamayerst55662]

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

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.

[SteviegtrParticipant @steviegtr]

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

Steve.

[William AyerstParticipant @williamayerst55662]

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!

[Gary WoodingParticipant @garywooding25363]

Posted by William Ayerst on 31/07/2021 21:13:55:

Do you know what thread the halfnut locking bolt will be, or what the gib locking screws are?

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

The gib locking screws are 1/4 BSF

[peak4Participant @peak4]

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

[Dave HalfordParticipant @davehalford22513]

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

[William AyerstParticipant @williamayerst55662]

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

[Richard MillingtonParticipant @richardmillington63972]

"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.

[Richard MillingtonParticipant @richardmillington63972]

P.S.

https://www.chronos.ltd.uk/product/2mt-drill-chuck-arbor-tapped-3-8-bsw-jt6-taper/

[William AyerstParticipant @williamayerst55662]

Thanks all – I guess that big locking nut for the half-nut / rack feed handle must be 3/8" BSF then?

Did my first horizontal milling in anger today and it went quite well. Not getting a super smooth finish on vertical milling yet (3/8" 4-flute endmill on brass rod) but lots of things to tweak. I'm starting from the beginning all over again.

One thing that is definitely jumping out at me is planning the order of operations – switching from drill to mill and back to drill again is quite a time sink!

[William AyerstParticipant @williamayerst55662]

Also, after trying to eyeball the centre of a piece of square bar with scribe marks and a needle-point wiggler and failing three times in a row to find the actual centre, I may be starting to understand the push towards a DRO …

[Richard MillingtonParticipant @richardmillington63972]

I assume so, it is on my 2A, can't remember a W/W thread being used apart from the drawbars. Measure it to find out for sure:

https://www.ring-plug-thread-gages.com/PDChart/BSF-thread-data.html

Brass, TBH can't remember milling any. When cutting brass on the lathe the tool doesn't have back rake, it may be grabbing and needs to be sharp.

[peak4Participant @peak4]

Posted by William Ayerst on 01/08/2021 20:54:11:

Also, after trying to eyeball the centre of a piece of square bar with scribe marks and a needle-point wiggler and failing three times in a row to find the actual centre, I may be starting to understand the push towards a DRO …

You could try one of these to be going on with.
Dearer options such as Starrett etc. are available too, if you have money burning a hole in your pocket.
https://www.arceurotrade.co.uk/catalogue/results.aspx?search=centre+finder

Bill

[Gary WoodingParticipant @garywooding25363]

Posted by Richard Millington on 01/08/2021 20:19:40:

"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.

For the Mk3 VH there is a small grub screw, just behind the quill lock handle, that pokes into a slot that limits the quill vertical movement. The nut on the front of the VH does nothing on my VH.

[William AyerstParticipant @williamayerst55662]

Peak4/Bill, I'm using the wiggler with a 1/4" ball head. Are these cylindrical finders better? In the meantime, should I be paying attention to it stop oscillating as my zero, or when it deflects?

Realistically I think I may have just fallen foul of expecting 1/4" square rod to actually be 0.250" .

I managed to nip up the bolt on the front of the vert head, it just seemed to be leaking oil through the loose bolt hole without it. Any ideas on what oil should go in it?

All the best!

[SillyOldDufferModerator @sillyoldduffer]

Posted by William Ayerst on 01/08/2021 20:54:11:

Also, after trying to eyeball the centre of a piece of square bar with scribe marks and a needle-point wiggler and failing three times in a row to find the actual centre, I may be starting to understand the push towards a DRO …

I'm a bit jealous of the fun William is having learning with his new toys! You can't say the process isn't interesting, but like magic tricks, finding out how it's done is an anti-climax, and then the task is just business as usual. Don't worry, next stage is making things accurately from someone else's plan, and beyond that is developing your own designs. There's always more to learn, and 3D CAD fills hours when the workshop is too hot or too cold.

Putting a DRO on a milling machine is a no-brainer, at least on the table. DRO transforms the machine, for example by eliminating the need to carry backlash correction and to carry 'how many turns' in your head. If a DRO is affordable, get one straight away.

With a DRO I rarely use anything other than a cylindrical edge finder and a needle wiggler on my mill. Cylindrical edge finders are easier to use than other types. I use it to locate a reference from two edges, and then work from that with the DRO. (Checking it often against other references.)

More often than not my needle wiggler is a dressmakers pin (a large pin with a plastic ball on the blunt end) and a blob of plasticine rather than the manufactured item. It's mostly used with a loupe to locate crossed lines or a centre-pop when no edge reference is available.

The accuracy of metal stock varies. Black Mild-steel is crudely untrustworthy. Bright mild-steel is much better, but varies between different strips, so check it. Not unusual for round rod to be a Reuleaux polygon (like a 50p coin) rather than truly circular. And I have some ¼" square rod that's actually a parallelogram. Ground stock is best for off the shelf accuracy, but expensive. Though Bright MIld Steel is usually 'good enough', a common first operation when milling is to start by cutting a reference surface rather than trust stock straight out of the box: if it doesn't have a reliable surface, cut one!

Dave

[Gary WoodingParticipant @garywooding25363]

I fitted a 3-axis DRO to my 2B and then added a DRO scale for the quill, which is surprisingly useful. As per SOD, I use an edge finder and work from an edge or a centre point (easy to find with a DRO). All my drawings are dimensioned accordingly – I never have use scribe lines or a centre-punch.

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