Dti Suggestions For Newbie

J

JPower6210

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Hi All- I need to buy a DTI and of course the options are endless. Any suggestions for a reasonable quality, reasonable price unit? What, as a beginner, should I be looking for in travel, resolution, etc. Thanks!

JP
 
DTI, is that a Digital Test Indicator? I'd much sooner have one with a needle, its so much easier to visualize the movement with a needle.

If a DTI is something else (I'm one of the old timers) my apologies, but I'll stand by needles.

Oops. I never thought of DIAL test indicator........mia culpa.
 
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I may not be calling it the right thing. But Dial Test Indicator is what I was thinking- with a needle- for indicating, trimming, etc.
 
I may be incorrect, but I was taught that a Dial Indicator (DI) generally reads .001" per graduation, and has 1/4" or more of movement. Dial Test Indicators (DTI) generally measure .0005 or less per graduation, and have limited measuring range.

DI's are used for "fairly accurate" work, whereas DTI's are used for really accurate work. When centering work in the 4 jaw chuck that needs to be dead-nuts accurate, I'll start with the DI (.001" graduations), and get the runout (needle movement) as small as possible. Then I switch to the DTI (.0005" graduations), and refine the centering of the workpiece until it shows as small a movement as possible.

DI's are available in digital flavors, but I dislike them personally. I prefer mechanical DI's with a needle, because it shows more than increments of .0005".

As for which ones to get? I use cheapie indicators from Harbor Freight. They're inexpensive (Around $14-15 or so) for a mechanical DI, and I have 3 or 4 of those. I bought a DTI from Little Machine Shop, 0-15-0 (max deviation of .03" on either side of zero), with .0005" graduations. I think it was around $30 or so. It's not a Starrett, but it works for me and has proven accurate enough for my shop. :) I have an old Federal DTI that I need to send off for repair, but the hobby fund is depleted.

I highly recommend a Noga type indicator holder, with the single locking knob. I bought one on sale about a month ago, and I love it. They're around $40 or so at LMS, and worth every penny. I've no complaints about mine. Beats the heck out of the non-articulated type that have two locking knobs. Indicators and magnetic base indicator holders are available all over the internet, and they're useful for far more than just holding an indicator. I mount my camcorder on them, my Nikon DSLR, use them to position chip deflectors when fly cutting, etc, etc. Handy little things.

Also, if you have a lathe, one of the inexpensive back-mounting magnets for a DI is a great thing. Sticks to the ways, you position the carriage, dial the indicator to zero, and you can return to the same point repeatedly. I prefer it to the depth stop on my lathe, unless I'm making multiples of an item. You can power feed against the indicator without crashing the machine (provided you don't crash the tool into the shoulder), but power feeding into a hard carriage stop gets expensive in a hurry.

Just my $.02
 
T Bredehoft said:
DTI, is that a Digital Test Indicator? I'd much sooner have one with a needle, its so much easier to visualize the movement with a needle.

If a DTI is something else (I'm one of the old timers) my apologies, but I'll stand by needles.
Click to expand...

Dial indicators have a plunger that moves in and out of a housing which is connected to a rack and pinion mechanism that converts the linear distance to a rotary distance on the dial face. Travel or measurement range can be as short as 1/8" or into multiple inches.

A test indicator has a lever which moves through an arc which is coupled with a mechanism that rotates the dial. The lever is adjustable for angle and in best practice, is adjusted so the movement is in the direction of the desired measurement to avoid a cosine error. Travel is limited to a few tens of thousandths or less.

Either can be obtained in varying resolutions. I have dial indicators with .001"/div., .0005"/div., and .0001"/div. and I have test indicators with .001 "/div. and .0001"/div.

Bob
 
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A lever arm indicator is useful if one is finding the center of a very small hole or a small feature where a plunger indicator will not fit, if you insist on making parts to tenths then by all means spend some money. Otherwise just use a plain cheap indicator.

If you are chasing tenths on a lathe you will not live long enough to get it right, buy a cylindrical grinder.
 
Cry once and get an Interapid, they are repairable, take a hit and keep working. 15 years or so I have had same one, hit the floor (concrete) twice, still accurate. Conversely you could buy the Chinese type for under $50, they are not repairable and do not last. Long Island Indicator has a great web page talking about the various brands, If I lost or ruined my Interapid 312b I would buy another in a minute.

michael
 
Compac, Alaina, Brown & Sharp, Tessa, these are all good indicators. I bought a few used one on Ebay, had to send most of the out to get repaired but it was money well spent. Tim
 
JPower6210 said:
Hi All- I need to buy a DTI and of course the options are endless. Any suggestions for a reasonable quality, reasonable price unit? What, as a beginner, should I be looking for in travel, resolution, etc. Thanks!

JP
Click to expand...

I'm going to assume you know what you mean when you say you need a DTI. In all likelihood this means you intend to use it on a mill to tram it or align your vise. You can get by with cheap Chinese stuff or you can buy good stuff that will last your lifetime and is repairable; I prefer the latter type. I would buy at least one that reads in 0.0005" units with a 0.060" range and it would be a Swiss unit like a Compac 214GA. Similar units are made by TESA, Interapid and Brown and Sharpe. My 214GA is going on 20 years now and it is buttery smooth, repeatable and accurate.

Watch ebay. If not, Amazon usually undersells most retailers.
 
JPower6210 said:
What, as a beginner, should I be looking for in travel, resolution, etc.
Click to expand...

Hi JP,

Some of that answer depends on what you need it for. Are you squaring a vice (or the entire table) on a mill? or checking lathe spindle run out? or something else?
I find I use a Dial Indicator almost every time in in the shop, but use the Dial Test Indicator only a few times a year.

-brino
 
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