View Full Version : indicating square

12-26-2006, 05:41 PM
I have a piece of brass that is 3/4" square and about 2 inches long. I have to borel it .5".
First How do you indicate it on the lathe? I seem to have no noom or the indicator and then it gets misalligned as soon as the next corner pops up and knocks it out again.
Second: I have a Vernon Jig borer. Shouldn't the head and table always be at 90 degrees? Shouldn't that be a viable way to drill this bore?? Or am I all off base???
Thanks in advance to all for their support and help!! I check the website about 4 times a day and have learned alot. I have accomplished alot with your help. Thanks in advance. Fred


Tin Falcon
12-26-2006, 06:01 PM
Not trying to be short or elusive but IIRC there was an excelent thread on indicating square stock in the lathe a few months back. Check the archive.
Here is the link http://bbs.homeshopmachinist.net/showthread.php?t=20974&highlight=centering+square+stock

Also I am not familiar with jig borers my guess is that you should check it like a mill and make sure it is trammed in and the spindle is perpendicular to the table.

12-26-2006, 06:07 PM
This problem got discussed a couple of months ago, I think, so a search of the archive ought to turn up something.

A couple of ideas come to mind. To do it in the lathe, I'd use a 4-jaw chuck and mount the indicator on the toolpost. Set the top of the work horizontal, or near as you can eyeball it, and run the indicator onto it using the cross slide. Retract the indicator using the cross slide, rotate the work+chuck 180 degrees, and check again. When the work is correct with that pair of jaws, rotate 90 degrees and start indicating the other two faces. When those are correct, go back to the first pair, because they'll almost certainly be off. But gradually zero in on it.

If I were doing it on the milling machine, I'd probably set up an angle plate with a block attached to it to give me a vertical 90 degree corner. Place a block maybe 1" thick on the milling machine table at the bottom of the corner, place the work into the corner and clamp it in place, then remove the block under it so there is clearance. Center over the work using an edge finder, etc., and drill/bore/ream the hole.

12-26-2006, 06:13 PM
thanks Guys. I figured a jig borer has a fixed head so it has to be 90 all the time to the table. It can't be changed (?). Oh well thanks for the sterling advice and Happy New Year. Fred

Tin Falcon
12-26-2006, 08:28 PM
Again not familiar with jig borer. My army training taught me to not expect what I do not inspect. Also when I worked in the precision shop where tenths count I again learned to check everthing and asume nothing. Just because the head is "fixed" does not guarantee it is the same as when set at the factory. It is likely to be ok. again you do not know unless you check it.

12-26-2006, 09:30 PM
The Vernon mill & jig bore is of one piece construction, and should be more than accurate enough for most purposes.


You will still be faced with centering it on the milling machine, and the procedure will be somewhat similar.

The primary question is what accuracy is required? For most purposes, a carefully laid out center punched spot can be easily located in the four jaw chuck using a wiggler.

12-27-2006, 09:48 AM
Thanks to all, I'll give it a shot today! My best to all Fred

Spin Doctor
12-27-2006, 04:54 PM
If you have access to Jig Borer* and need stuff done absolutely on center, straight and square they are the way to go as long as the work fits in the envolope. For checking square yo need something you know is square to check against. An inspection grade Angle plate would be good as would a granite square like those used to check CNC machines. An important thing to consider when setting up a job in a Jig Borer is to make sure that the angle plates and other fixturing you use does not contribute to out of square conditions. When I was working I occasionally had to bore out, sleeve and rebore the housings for precision spindles. This often required the use of thin pieces of shim stock to get everything all squared up aqainst the angle plates as they were not really quite up to the accuracy required. They were fine for general use but not that.


* You lucky devil

12-28-2006, 09:00 AM
Did it...ended up using the lathe. Ahair off here and there. Still makes more sense to me to use the jig borer though. Thanks Fred