dro errors

[steamjohn248]

Beware complacency.

There was some discussion a while back about read outs and whether they could be relied on, "do you believe it implicitly or do you check".

Well I was one of the "I believe it school", after all it cost the thick end of £1100. (and that was ten years ago).

Today, jig boring for the bushes in a 14" long con rod, profiled from a bit of 1" thick plate, including the holes, (undersize to allow for small errors) the small end hole seemed to be 'out'.
Never mind, had allowed for that so away we go, take the holes out to size press in the bushes and fit it on the loco.

Problem: the dead spaces in the cylinder seemed uneven, like not much at one end and lots at the other. Rod off and checked with the big vernier, oh dear 070" too long. Clamped the vernier on the table of the mill and sure enough 070" out.

Got the book of 'destructions' out and fiddled about with all the buttons, cleaned the head and bar etc. and got down to 001" over 14", better, but not as good as it says on the tin.

Phoned the makers who said our venerable old Bridgeport table probably "rocks" a bit which might account for the remaining error.

Be that as it may, from now on I'm in the "always check it with the mark one eyeball" school of thought.

(Fortunately the good old eccentric bush came to the rescue).

Be warned

John

[circlip]

Yes John, and I was called down from the ""OTHER" side for saying check it longhand anyway. However, NOT gloating, it just goes to show that if there is another way to check, which only takes a few minutes, then why not use it? It certainly saves a lot of head scratching when you've added a few more bits to the equation. THE ONLY TYPE OF READOUT I WOULD TRUST IMPLICITLY WERE THE OPTICAL ONES used on the Bridgeport BEFORE the mods to electronics. Just as an aside, another thread I was called down on with regards to electronic centering, on an American site, the same unit was being pedalled, and how wonderful etc. some other loony remarked on the same point with reference to the height oh the camera above the workpiece and how the position could be affected by changing the height? Two of us got it wrong then? INDEPENDENTLY. Electronic angle finders also suffer when the battery is running down but that's a bit subtle, the angle only differs by a couple of degrees,initially. I'm all for advancement but lets WALK rather than gallop,- the old bull and the young one? Best regards John, Ian

[mutley]

Hi Circlip
You werent called down from the 'other' side. I mearly remarked that you and another member were hounding people for their method and choice of working.
I dont think its fair to blame mechanical wear on the DRO.
I have optical scales on my DRO what type of scales are we actually talking about here, the cheaper chinese units that are self contained or modern optical glass units with an external head unit?

Andy

[havoc]

That's why there is something called "calibration".

[3405jimmy]

Let’s see one error in 10 years, I’ll go for that. Before I got the DRO I could generate an error about every 11 seconds.

The view from the dark side?

[ausdan]

If there one thing I hate about a DRO, it is that I don't have one on my Lathe

how ironic though...by any chance do u use a steel rule that has been calibrated? or do u assume its correct.


Back on subject I would suggest, before starting a high priced ( or tolerance) job on your mill, is to check the extreme movements and the accuracy of the DRO, know the limitations before you start.You may even over time, learn the limitations of your own equipment...Mind you I still got a long way to get to that standard, mine DRO is accu-rite brand with glass scales works far better than I can, I cant see .0005" but my DRO can - I have no trade or formal teachings and the DRO helps you get there so much faster.

Because if we blame it on every DRO every made, the world will come to screaming halt

As Jimmy said
Let’s see one error in 10 years, I’ll go for that. Before I got the DRO I could generate an error about every 11 seconds.

so true

[circlip]

Yes Freddo you're quite right it seems that people have an inability to read the written word and understand it. For everyone who could not read the small print of my answer to John's original post I have changed to UPPER CASE my comment on readouts, not D readouts however. Anything to make reading easier.

[steamjohn248]

I didn't want to start World War III, it was just a light hearted warning to other DRO users to cross check. For the record mine is a Newall and was top of the range when purchased, (it cost a damm sight more than the Bridgeport) and has never put a digit wrong till last week. I'm sending the head back and they will exchange it. (and no one blamed the DRO for mechanical wear). (or anything else).

[tcase]

Whatever the limits of he readout system used, a major gain is that you no longer need to worry about backlash.

[ianengr]

Greetings all,

I have often wondered if it would be possible to mount a DRO on a milling machine in such a way that the scales were referenced from the column or at least a separate linear slide mounted on the column so that any horizontal movement of the knee (X Y axis) when raising,
lowering, tilting or movement from cutting forces could be detected and corrected. It can usually be checked between machining operations without much trouble, but can sometimes be quite difficult and there's not much point having zero backlash if the work piece goes side-ways every time you put the periscope up or down.

Mounting a scale at the back of the lathe parallel to the bed-ways that registers cross slide movement would surely be preferable to the vulnerable position adjacent to the slide itself. (Perhaps some sort of bell crank or enclosed cable arrangement could be used)
However, having said all that, I've never set any of them up - so there may well be a valid reason why I've never seen it done that way.

Another item on the problem solving and things to do list.

Ian.

[freddo]

May 21, 2008 21:57:38 GMT tcase said:

Whatever the limits of he readout system used, a major gain is that you no longer need to worry about backlash.

Nice thought, but unless you were cranking the table against the thrust of the milling cutter, and just been doing the back-and-forward wiggle wiggle till the DRO says spot-on, the backlash will catch you out when the cutter grabs the workpiece - false security again I fear. But then again, what do I know, I just make choo-choos the old fashioned way.

Freddo

I can't resist adding that my cheap Chinese mill is rigid enough to allow "climb" milling - unlike a well worn and polished deckel or bridgeport. ;D