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Thread: centering tool for mill
03-10-2005, 10:05 PM #1
Here is a tool I built to center things in my mill. As all of you who have tried to center stuff with a dial test indicator, the danged thing is backwards part of the time and it is easy to lose track of which way the needle is moving if you use a mirror. This device holds the test indicator horizontal so it is visible and allows fine adjustment. It is based on one described in Machinist's Workshop Magazine by Glenn L. Wilson, but significantly modified by me. My mods include the dovetail slide and the fine adjustment.
The above pic shows it in use centering a piece in a chuck on my rotary table. Below is the right hand side showing the tool up close. The head fits in a half inch collet and has a female dovetail with gib to lock the sliding male dovetail in place. You can see that the dial test indicator is held by a small block attached to the sliding dovetail with a thin piece of steel which serves as a spring hinge. Major adjustment is by the sliding dovetail. Fine adjustment is by the large adjustment wheel on the block that holds the indicator. It has a cam surface which rubs against the end of the dovetail piece and slightly bends the spring hinge for fine adjustment.
The pic below shows the other side of the device with the dovetail clamp to hold the test indicator.
Yes, I know I could just go buy a co-ax indicator, but this was free, fun, and educational. I learned to measure dovetails in the process, as well as threads by the three wire method, and the design and construction phases were both enjoyable. Retirement sure is nice!
03-10-2005, 10:13 PM #2
Quite nice work! Loved the mini-dovetail.
03-10-2005, 11:03 PM #3
Stu, that's the bee's knees! I would love one for the HBM at work.
03-10-2005, 11:29 PM #4
Stu looks great...
However, I heard a rumor that may or may not be true...The rumor is that a test indicator with more than 30 degrees of flex on the needle is exponentially inaccurate past those 30 degrees. I see yours at damn near 90 degrees.
03-10-2005, 11:45 PM #5
Rugby, I think the problem is with the indicator tip at an angle of more than 30 degrees to the surface being indicated. As shown, the indicator and the dro are in agreement when I move the table.
03-11-2005, 01:10 AM #6
That's too cool for school. I might have to steal that idea [img]smile.gif[/img] .
How large of swing will it sweep? Have you used it to check tram (I'm guessing you could bu using the back dovetail on the DTI)?
03-11-2005, 01:23 AM #7
I like it. Cool concept and great execution.
03-11-2005, 01:40 AM #8
Stu, thats really nice and almost a direct copy of the indicator setup that I got with my SIP jig bore. Much better then the Indicol thing that they sell. Good work on the dovetail part. Now I want one for my BPT. Tool up and mass produce them for about 150.000 to 200.00 with out the DIT and you will sell a bunch. Nobody does innovating tool design these days and that is something a lot of shops and machinist would like to have. Nothing more infurating then an indicator setup that you can't trust. Years ago I built my own tramming indicator setup to use on VMC when squareing them up and my customers always look at it and say were did you buy that?, it's really ridged and I just replied that I built it. I got tired of useing the light weight stuff avalible and wanted something that woulden't deflect. I want one of yours with a .5000 shank. Were do i place the order.
03-11-2005, 01:57 AM #9
Stu, your craftmanship is excellent. Really a nice looking piece and very practical. Thanks for sharing it with us.
03-11-2005, 12:42 PM #10
You guys are going to give me a swelled head. Thanks for all the kind words.
Jon, as set up, it swings about 5 1/2 inches, but with the slide reversed it would swing 10 inches. It could be used as you suggest to tram the mill head, the only drawback being that the indicator dial would be vertical and I would be back to misreading the indicator with a mirror on the back side. Hmmm, now that you mention it, an accessory could be an adapter to hold the indicator horizontal by the back dovetail. If you will excuse me, I gotta go back to the shop now. [img]smile.gif[/img]
03-11-2005, 12:49 PM #11
I looked at this idea this morning and thought what an improvement it was on a co-ax indicator.
I'm sorry but I'm not a big lover of these co-ax indicators, they are far too long and bulky.
Later on today i had to go out and see a customer, they were clearing some stuff out and believe it or not there was one of these in amongst the bits.
Very slightly different to yours in that the dovetail is screwd to a large ISO 50 taper and the attachment is made to take a normal dial gauge and transfer it to vertical via a bell crank
Very nicely made and Russian in origin.
Also picked up a Russian centreing microscope on an ISO 50 but the shank is interchangable.
If it glows in the dark it will help it
03-11-2005, 02:42 PM #12
Concerning tramming; I think you could adjust the indicator spindle to a "flatter" angle(45 degree or so) to contact the table. The inaccuracy from the spindle being at an angle shouldn't matter, as you would only be looking for the same reading in the different positions; not the amount of movement.
For my use, I would consider making the holding spindle a stepped design; 3/8" and 1/2", as those are the collet sizes that I use most.
Thanks for sharing!
If the forum is lacking posts for a while, it may be that several members are busy building a copy of your design!
03-11-2005, 03:16 PM #13
Stu- very nice job of machining and adaption