# Pump Center



## Tin Falcon (Nov 4, 2007)

*Guys this is what I use to center a punch mark or small hole in the 4 jaw chuck. the one I use came with a box of tools I bought. I decided I would sketch it up for anyone that wants to make there own. great simple starter lathe project . I am sure there are many variations to this. If your are sure of your measuring skills and  fits you can start with a 7" piece of drill rod and make the little part first. the way I wrote it up gives the builder an opportunity to test fit the small piece before taking it out of the lathe and you can always bore the hole in the long piece  or use a "D" bit if a reamer is not available. Most of the dimensions are not critical the important thing is the two pieces slide easily together before assembly 
Tin*


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## kjk (Jul 20, 2010)

Tin Falcon: Is there a larger version of this image somewhere on the site?


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## TroyO (Jul 20, 2010)

There's full plans for a similar one on the Projects in Metal website.

http://www.projectsinmetal.com/free-project-plan-spring-center-metal-lathe-mill/

You do have to register now (Free), but there's a couple of nice plans/ideas on there.


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## kjk (Jul 20, 2010)

Thanks for that TroyO. I've registered and you are right - there are lots of interesting bits there.


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## mklotz (Jul 20, 2010)

While a spring-loaded pump center is the preferred way to go, the spring-loading is not absolutely essential.

A simple rod with a 60 deg point on one end and a 60 deg center hole in the other end supported by a center in the tailstock will work if the workpiece isn't too far off center when you start.

Even simpler is a thinner, more flexible rod held in the TS chuck. As long as it can bend to follow the (slight) eccentric movement of the workpiece, it will get the job done.

In some cases, one can use the pointy end of an edge finder. Grasp in TS chuck with point in hole-to-be-centered and adjust chuck until there's no runout. This approach doesn't even require a DI. You can detect the misalignment with your fingernail or, if you require more precision, simply use a mike to measure across the interface between the point and the body of the edge finder. When that measurement is equal to the body diameter, you're done.


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## wheeltapper (Jul 20, 2010)

Hi
this is my pump centre, 





it's a dual purpose one, the blunt end is centered





so with a centre in the tailstock it's a wobbler and with a chuck in the tailstock it's a spring tensioner for a tapholder





very useful little gadget.

Roy.


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## kjk (Jul 20, 2010)

I like the simplicity of Wheeltappers design - I'll take a shot at one tonight if I can find the bits in my inventory. Thanks everyone for taking the time to reply.


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## wheeltapper (Jul 20, 2010)

cheers for that :bow:
you'll notice a grubscrew in the blunt end of the pointy bit ( very descriptive here :big.
there is a flat filed on the spindle , it stops about 2mm from the end. the grub is to stop the pointy bit going into orbit.

Roy


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## Tin Falcon (Jul 20, 2010)

sorry I never went back and fixed that. Can not seem to find that file to updated in a better format . but it looks like folks have taken care of you. 
Tin


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## zeeprogrammer (Jul 20, 2010)

I'm absolutely confused.

Why is it named a 'pump center'?
And I still don't know how to use one, when to use one, why to use one.
(Not that it helps if I did...I ain't got one.)

Thanks for the pics wheeltapper. I think I understand the last pic...center in the tailstock against the 'pump center' blunt end...pointy end of the 'pump center' against the tap handle. Spring provides pressure without having to adjust the tailstock. Is that right?

I'd be interested in knowing more.


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## dreeves (Jul 20, 2010)

Zee, I knew you had it in ya. :big:


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## mklotz (Jul 21, 2010)

Carl,

Imagine you have a workpiece in the 4J with a hole you want to center. Insert the male end of the pump center in the hole and support the (spring-loaded) female end with a center in the TS. The spring-loading keeps the male end pressed into the hole. As you rotate the chuck (and workpiece) the male end will oscillate due to the hole misalignment. Place a DI with an elephant foot against the male end to read oscillation and adjust jaws to center work.

It's discussed in my writeup of 4J centering.


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## minerva (Jul 21, 2010)

Carl
to illustrate Marvs description here's a photo of setting up the eccentric strap on my latest effort







Clock the pointy end for zero run out and Bobs your uncle! As a newbie to these techniques I have found it to be the simplest way to go for 4J centreing. I must say I haven't used it for tapping yet but can see the advantages especially with small taps 

Regards 

TerryT


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## T70MkIII (Jul 21, 2010)

Thinking out loud here - I guess if you're not after a huge degree of accuracy with the 4J you could just run the TS centre into your punch mark or centre hole, with a bit of dychem or chalk in the hole, and hand turn the chuck. The dychem etc would rub away letting you know how close to centre you are. Repeat as necessary. Interesting to confirm with a pump centre or edge finder to see how close you could get.


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## zeeprogrammer (Jul 21, 2010)

Very clear. Thanks very much everyone.

That also explains the 'center' portion of the name.
'pump'? Because of the spring?


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## tyleryoungblood (Jul 21, 2010)

Yep Zee, i believe the "pump" is in reference to the fact that it is able to move back and fourth along the Z axis. It's other name is a "Spring Center", which is slightly more clear. 

Here's the one I made. As mentioned earlier, plans are available on ProjectsInMetal.com






I use it more for tapping with small taps than for centering, and I don't just use it on the lathe. Here's an example of me using it on the mill. It really helps keep the tap aligned. I've never broken a tap while using it. 






This was actually the first project I ever made on the lathe and it's become one of my most regularly used tools. I can't believe how often I use it. You won't regret making one!

Tyler
ProjectsInMetal.com


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## winklmj (Jul 21, 2010)

One of my first projects too:

Parts:





Assembled:





That ProjectsInMetal design looks really nice--especially for tap holding. And I like the tailstock flag as well. More stuff for the projects to-do list.


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## zeeprogrammer (Jul 21, 2010)

Definitely a handy tool to have.

In my short hobby career I've already had several opportunities where that would be helpful.

Lathe certainly, but my mill doesn't have the room.

Is there any reason that would dictate the overall length of the pump/spring center other than, I guess, the spring?


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## Tin Falcon (Jul 21, 2010)

> Is there any reason that would dictate the overall length of the pump/spring center other than, I guess, the spring?



Z: it depends on the intended use. In my experience a pump center is relatively long and thin and used to cent a part in a 4 jaw chuck and there is only about 1/4 inch or so of movement. My spring center loaded tap guide needs more travel as to guide a tap and is larger diameter. I would think with a little creativity one could make one to function for both uses. 
Tin


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## ksouers (Jul 21, 2010)

Zee, for tapping I use a short piece of broken end mill that was ground to a point. You could also make one out of drill rod or even mild steel.

It's the piece just above the V-blocks.







I use a longer piece of drill rod, about 8 inches, for a pump center. No springs at all in either one. For the tapping center I do have advance the quill each turn. Both have served me well for several years, though I've had an itch to make a spring-loaded tapping center.


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## mklotz (Jul 22, 2010)

zeeprogrammer  said:
			
		

> Definitely a handy tool to have.
> 
> In my short hobby career I've already had several opportunities where that would be helpful.
> 
> ...



Room under the mill head is always a problem. The spring-loading afforded by the pump center isn't really needed for guiding taps. A simple swivel will work as well or better.

Look at the tap wrench on the far right in this (repeated) photo...







It's purpose-built to be as low profile as possible. The tap fits deeply into the body to reduce overall length. The pivot rod fits into the chuck so the lateral support mechanism takes up as little vertical room as possible. The collets allow it to accept a wide variety of tap sizes (though I would recommend one of the models on the left for taps smaller than #4).


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## SAM in LA (Jul 22, 2010)

With all the talk about pump centers I decided that I needed one too.

I modeled mine after the one on the "Projects in Metal" website.

I changed dimensions to accommodate the material on hand.

I had a piece of Stainless Steel, I do not know any details of it though.






I turned a 3/8" and 1/2" step on the end along with a centerdrilled spot on the end.

If you noticed, the tapered end appears to have zebra stripes on it. The next photo shows the stripes better.






It took me a few minutes to figure out why the stripes were there.

My lathe does not have a compound tool rest on it so I have to rotate the cross slide to cut the taper. The stripes are the same pitch as the cross slides screw.






My guess is the screw is bent. This screw is supported by bushings and there is no thrust bearing. One of my future fixes are to make a split nut and install roller bearings and a needle thrust bearing. My repair list keeps growing.

Thanks for stopping by,

SAM


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## ozzie46 (Jul 22, 2010)

Sam, Grizzily 10 x 22 s seem to be prone to this kind of markings on the work. I have checked lead screw, gibs, and other things and I am coming to believe it goes back to the 2 bolt compound tighten ring instead of have 4 bolts to hold the compound 

 The yahoo 10 x 22 forum has people complaining about it too. So don't be in a rush to blame the lead screw. It might be something else. Just my 2 cents worth.

 Ron


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## SAM in LA (Jul 22, 2010)

Ron,

Thanks for the information.

I have a 1994 vintage ShopTask Lathe/Mill.

I do not have a compound on this machine. I wish I did though, it would make cutting short tapers a lot easier without having to indicate the cross slide back into square with the lathe ways.

Before I got it, it has seen a lot of use and abuse.

I have replaced the bearings in the lathe head stock and still need to do the bearings in the mill portion. The lead screws on the lathe are supported by bushings which I will end up replacing with bearings. I also plan to make up split nuts to take some of the sloppiness. Sorry the proper word escapes me at the moment.

Thanks

SAM


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## ozzie46 (Jul 22, 2010)

Is "backlash" the word your looking for?

  I know what you mean about words "escaping you ". I don"t know how old you are but it seems they "escape me " more often as I get older. :big: :big: :big: :big:

  Ron


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## SAM in LA (Jul 22, 2010)

ozzie46  said:
			
		

> Is "backlash" the word your looking for?
> 
> I know what you mean about words "escaping you ". I don"t know how old you are but it seems they "escape me " more often as I get older. :big: :big: :big: :big:
> 
> Ron



Ron,

Backlash is exactly the word I was looking for.

SAM


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## Omnimill (Aug 17, 2012)

Old thread this one but thought anyone stumbling over it may like to see this as well, looks easy enough to make:

http://www.chronos.ltd.uk/acatalog/threading_accessories.html

http://www.chronos.ltd.uk/acatalog/info_318221.html

Vic.


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