Setting up to a mark in 4 jaw chuck

[Ross_macker]

Hi all,

I have just started building my second motor which is an Elmer's twin wobbler. When i went to set up the cylinders in the 4 jaw chuck i had a great deal of difficulty. The first one i just used a center punch mark and used the tail stock center to line up with the mark. On the second one i used the drill press to center drill the mark then clamped it lightly in the chuck and used a dial indicator to check it was straight. Both cylinders came out slightly off the mark (about .25mm). Is there an easier way?

thanks
ross

 

[Engine maker]

If I have to drill or bore a hole in a block that I'm going to put in a lathe I first use my mill to accurately center drill and drill a small hole which I then ream too say (1/8" or 1/4"inch) in the piece. With the mill you can get it very accurate and aligned perfect. Then I slide a ground dowel pin in the hole. This should be a nice fit in the hole. Then it into the lathe where it can be indicated the pin with a dial indicator till it's on center. Then just pull out the pin and start making chips. This system works great on intersecting holes.

Jim

 

[gbritnell]

Ross. However you can put a small dimple in your part do it. By that I mean you can scribe lines on your part and take a sharp punch and just dimple it ever so lightly or put it in the mill, if you have one, and center drill it with a #1 center drill. Now mount your part in the lathe, put a wiggler in the tailstock chuck and move the tailstock up to your part so you can put the tip of the wiggler into the dimple. Mount a dial indicator into whatever you have to hold it and put the tip of the indicator against the wiggler. Now turn the chuck by hand and adjust the jaws until there is no runout on the indicator.
gbritnell

 

[arnoldb]

Hi Ross

What you need for this is (ideally)a pump center - which you most likely don't have yet. (put that on your to-build list ). If you have a spare tailstock center (that have a center hole in the back) that will work.

DON'T try and center drill the workpiece - just center punch it.
Set the workpiece in the chuck, and center it as closely as you can by eye (or -even better- using the tailstock method you described in your post) but just lightly clamp it.

Then put the spare center with it's point in the punched hole, and it's tail on your normal tailstock center and very lightly tighten up the tailstock.
Use your dial indicator close to the center line on the side of the supported center close to the chuck. Turn the chuck (by hand!) and the indicator will give you minimum and maximum readings. Calculate the reading that would be half-way between the minimum and maximum readings. Then use opposing jaws to adjust the workpiece to get to the half-way reading.

Hope this makes sense ;D - initially it takes a while to do, but with some experience, it becomes quicker.

While I was posting this, gbritnell also posted; that's about the same procedure, but I doubt it if you have a wiggler yet...

Regards, Arnold

 

[mklotz]

A pump center is nice but you can get by with the most fundamental of wigglers...

Simply take a length* of steel rod and turn a point on it. Grasp the unpointed end in the tailstock chuck and put the point in the punch mark (a small center hole is better IMO). Fit your DI with a flat tip and put it against the rod close to the pointed end. As the work is turned in the chuck the rod will deflect due to the mark offset and that offset can be read on the DI.

--
* Something around 12" is good but can be shorter on smaller lathes. The important thing is that, whatever length, the diameter is small enough that the rod can deflect easily.

 

[firebird]

Hi

I could never get on with a 4 jaw until I made a pump centre. I have since made a simple post that mounts on the rear of the cross slide (I have a myford lathe) that has the necessary mounting bracket for a DTI. It all sits in a box behind the lathe and can be installed in minutes. Centreing a piece in the 4 jaw chuck, round, square or any other shape is now a doddle. Its well worth taking the time to make one. If you have a tool thats quick and easy to use it makes life very simple.

Cheers

Rich

 

[Ross_macker]

Hi all,

Thanks for the help. I will have a more of a look into it this arvo. I have had a look around on the net but have not came up with results on the wriggler or center finders. Does any one know where they can be purchased in Australia? I will post some photos of this motor as i go.

thanks
ross

 

[Majorstrain]

Here you go Ross,
this is the Ebay item number 400077970037
and link Bid http://cgi.ebay.com.au/WRIGGLER-CENTER-FINDER-SET_W0QQitemZ400077970037QQcmdZViewItemQQptZAU_BnI_Woodworking_Metalworking?hash=item5d26815a75#ht_1342wt_850
or buy it now $32 + $6p&p http://cgi.ebay.com.au/WRIGGLER-CENTER-FINDER-SET_W0QQitemZ150221187018QQcmdZViewItemQQptZAU_Toys_Hobbies_Model_Kits?hash=item22f9e167ca#ht_1518wt_850

Location : South West Goulburn, Victoria, Australia
Ebay store name : The Engineers Shop

Cheers
Phil

 

[Ross_macker]

thanks for that
will keep an eye on them
;D