Pump centre

I would find a "pump centre" or "Sprung centre" very useful for locating centre drilled dots for referencing for milling. By this I mean a sleeve max 10mm diameter with a true sliding centre point protruding from it which is sprung outwards with something to retain it in the sleeve. In use one chucks the sleeve in a collet and brings the chuck down until the point clicks into the hole one wants to locate.  At the moment I fit a rod with a centred point in the ER collet so it can slide with a little friction but this is a bit hit and miss.

Does anyone know of such a device made commercially please?

Edited By John Haine on 22/11/2021 10:50:25

Hi John,

I believe that Arceuro sell them.

For another John!

[Sorry] Not answering your purchasing question, John

Here is a useful discussion from the NAWCC : **LINK**

https://mb.nawcc.org/threads/making-a-pump-center-for-8mm-face-plate.92078/

MichaelG.

In his book "A Model Engineers Workshop Manual" G H Thomas discusses similar devices (page 27) and describes a neat design. I made one 20 odd years ago and use it from time to time. Like all GHT designs, it works beautifully. Could be made in an hour. GHT mentions that a commercial device used to be made by Starrett.

Mike

Most co-axial centre finders come with a point as well as the usual arms though it does mean raising the head a bit more than a simple device it doe shave the advantage of giving a reading as to how far you nee dto move the table to get the part true

If you don't want to make, you could use one of the gadgets meant for supporting a Tap in a machine.

I have a set of six, 3 male, 3 female centres. I think the trade name is Tap Tru.

Arc sell male ones as Spring Tapping Guide

The Micro one (060-250-03100 ) has a 4.75 mm dia pin, while the larger one (060-250-03200 ) has 9.5 mm dia pin.

Howard

Thanks for the responses. The ArcEuro one would be perfect but alas has a 12.7mm shank but my max ER collet is 10mm. I do have a 12mm BT30 collet but that's still too small. Oh well, out with the drilles and reamers and make one I think.

I made and use GHT's "wobbler" device which I think works in a different way from the one mentioned by the OP; in use it is supported by the tailstock centre.

I would like to find the Starrett version in their catalogue - does anyone know the correct name, please?

.

I fear there may have been some confusion …
Starrett’s current offerings are here: **LINK**

https://www.starrett.com/category/111603#currentPage=1&displayMode=grid&itemsPerPage=12&sortBy=wp/asc

… none of which could realistically be described as a ‘pump centre’

[or even a ‘pump center’]

MichaelG.

.

Note: __ The version used on the Watchmaker’s lathe is typically manually controlled rather than spring-loaded, but this gives a good idea of the principle:

https://www.snclocks.com/TechnicalInformation/Tid-Bits/Tid-Bit-8-Drilling-tiny-holes/i-xHJcJ97

Edited By Michael Gilligan on 23/11/2021 00:03:17

MichaelG:

Thank you! I suppose it is possible that GHT himself was confused.

I think his idea of a pump centre was a strongly sprung device which would compensate the expansion of work between centres.

If a commercial available pump centre has too large a shank, it may be possble to reduce the diameter slightly, to 10 mm to fit into your collet.

If the body is case hardened, it may well need a carbide tip to cut it. Removing 1 mm a side will probably remove the case, but since it will only be gripped, wear of the OD is unlikely.

The red hot wire coming off can be quite thrilling to watch!

Howard

My punch was made by Eclipse and known as a spring centre punch,I inherited mine from my father ,he used it but I never found it much use ,I prefer the fine prick punch followed up by a centre punch,

That's not the same thing as the pump centre in the first post though