Accuracy on the lathe

[chucketn]

In a post about lathe milling attachments, a comment was made about using dial indicators to make accurate cuts on the lathe. I for one could stand to learn how to be more accurate on the lathe (no DRO on the lathe).
What is your technique for using dial indicators on the lathe to make accurate cuts. Pictures please!

Chuck

 

[Shawn]

I have a set of dial indicators setup on my lathe, the one for the cross slide gets used every time I use the lathe.

 

[Teus]

I have a set of dial indicators setup on my lathe, the one for the cross slide

Great tip Shawn very useful. Thm:

I gonna make a same setup, Thanks.

 

[lohring]

I used a carriage travel dial indicator for years. A fancier version that doesn't cost much more uses digital scales.

Lohring Miller

 

[chucketn]

Now THAT"S what I'm talkin' 'bout! 2 hours since the origional post and look what we got!

Lohring, can you give more details, like brand, source, readout, cost?

Chuck

 

[Propforward]

I have a set of dial indicators setup on my lathe, the one for the cross slide gets used every time I use the lathe.

Holy moly! What a great and simple idea - I will be rigging something like this up for sure. I can see some dimensional improvements coming quite quickly with this technique. Big thumbs up! Thm:

 

[lensman57]

Hi,

I use long travel dial indicators on my lathe, I find the lathe dials quite accurate but compensating for the back lash is a problem at times, so the indicators come in handy so long as they are set perpendicular to the ways or cross slide and the measuring surface is flat. The cheap Chinese made digital ones are quite good as you can zero them on the move and they measure the distance accurately. When not in use you can just remove them, this is an advatage over the fixed ones IMHO.

Regards,

A.G

 

[Jeff-in-PA]

I used a carriage travel dial indicator for years. A fancier version that doesn't cost much more uses digital scales.

Lohring Miller

Thanks for posting that Lohring.

I just found these on ebay for cheap, item 230747956665
35" travel
http://www.ebay.com/itm/230747956665?_trksid=p5197.c0.m619

12" travel , item 230899207877
http://www.ebay.com/itm/12-DIGITAL-...877?pt=LH_DefaultDomain_0&hash=item35c2aa4ec5

Are these similar to your set up?

Thanks
Jeff

 

[Shawn]

The back of the South Bend cross slide has two threaded holes for attaching a taper attachment. It took about a half hour to thread a rod and attach the indicator. The indicator can be rotated out of the way in 2 seconds by releasing the bolt on the 1" square tube. The only thing I have to remember is to divide the depth of the cut by two before cutting, otherwise I end up taking of twice as much as I want. I've learned this the hard way more than once the first few times using it

 

[Fluffy]

Chuck,
Here is a simple little clamp that I have used for years to hold a 0 to 30 mm dial indicator to measure the saddle movement when accurate length/positioning is required. Made to suit my lathe & has worked well. The movement of the indicator must be parallel with movement of the saddle.
The indicator is used on the tailstock end of the bed as I do not have enough room to fit the clamp at the headstock end.
If you are to use a similar method to measure cross slide movement remember that you will be working on the work radius & whatever movement is set on the dial indicator will be half of what will be removed from the work diameter.
The secret to accurate machining is to continually measure the surface being machined. When turning the finished diameter, take a cut long enough to enable the measuring tool to be accurately used, stop, retract the tool, & measure. If OK continue, if not adjust & repeat. The more the surface is measured, the less chance of turning undersize.
Regards,
Don.

 

[Ken I]

Before you reach finished size, determine what depth of cut you will be taking for the final pass and "practice" that depth shortly before you reach finished size (ie a depth of cut that gives a good finish) that way you can predetermine the difference between input and actual and get to an exact size before the final cut - this process will get you to the exact size you are aiming for.

Clear as mud ?

Ken

 

[kvom]

At school we used a "mighty mag" magnetic holder to attach a DI to the lathe bed for measuring travel.

 

[lohring]

Now THAT"S what I'm talkin' 'bout! 2 hours since the origional post and look what we got!

Lohring, can you give more details, like brand, source, readout, cost?

Chuck

An article on the details should appear in Model Engine Builder soon.

Lohring Miller

 

[Forestgnome]

"The secret to accurate machining is to continually measure the surface being machined"
Normally you shouldn't have to measure too often. In my mind, the secret to accurate machining (in terms of hitting a diameter) is in knowing that lathe tools don't always cut to the DOC setting. Each tool cuts differently, and also cuts differently depending on the DOC. When approaching the final diameter, I make sure I have two cuts left, one to measure the effect of the last DOC, and the final pass. So say I'm turning a 2" dia piece down to 1.00". I might stop at 1.030" after using a .050" DOC, then I'll divide the remainder by two so I'll have two cuts at .015" DOC. I make one pass and measure. I may find I've only cut .014, so the next cut will be adjusted by +.002 to .017". This technique kills it every time, HSS or carbide.

 

[Tin Falcon]

IN my USAF machining classes we used micrometer stops. Layout to get close . measure cut measure .. use the micrometer stop to set adjust the finish final cuts.
tin

 

[gus]

Here is how a good friend suggest if O.D. n I.D. is very critical.
When you are with last 10 thou. Use a hit list to track cut depth(no. of division advanced ) versus new dia.Take note of div advance and dia reduced.As you approach last two----three pass,you may decide to go for 1 div or 1/2 div. Tool bit is best ground sharp before last few cuts.If you need an urgent pee break,go. Its the last final cut that decides who won and who lost.The scrap bin or the turner.
Good Idea to take out all slacks on the slides.

As we age we get forgetful.W/o the hit list and after answering the handphone,it is usually disastrous.Make it a point to zero dial after every pass.
A dial gage mounted on to read tool bit advance helps for those who has yet to buy a DRO. My Sakai ML 360 is just too small to accept DRO.Plus the fact ,my three open sided balcony is no 100% storm proof. DRO cannot take the mini rain droplets.

Ever since I used hit list,hitting the required OD or ID was a breeze. Belief idea Tubal Cain for the hobby machinists .

 

[starnovice]

This is a good point Gus. I have found it also helps you to learn the quirks of you machine. Sometimes 1 div does not equal .001 and this will show that very quickly.

Pat

 

[Forestgnome]

"Make it a point to zero dial after every pass." My take is this is a way to add error. Just write down the last setting.

 

[Tin Falcon]

The most important aspect of accurate work is accurate measuring. Even on a cnc with pre programmed moves the machine would have quirks depending on the time of day phase of the moon wind direction etc. and of course some tool wear.
A tolerance of +- .005 is fairly typical of most general lathe work, but it is possible to work +- .0005 if you measure and plan carefully.

OMHO a good way to stay out of trouble is use a digital caliper and a micrometer that reads in tenths. why both ? the digital will get you into the ball park and the micrometer will get you to home plate.
a caliper will typicaly get you withing a couple thousandths but will not get you within a tenth. the mic reads in tenths accurately but it is possible to misread the lines and be off by .025 in DAMHIKT.
like others have said practice, and experiment getting the best finish and know how much material needs to be left for a finish cut.
get and keep a notebook.
Tin

 

[goldstar31]

Hoorah, Tin, for your comments. Someone had to tell people the cold fact that a tool that will measure in thous- which will probably have a tolerance of plus or minus a thous or worse but 2 thous. And 2 thous might be too tight-- or a rattling bad fit.

So far, no one has mentioned checking your inspection/measuring tooling against a standard.

Do you know how accurate your tools actually are?

Thank you, Tin, for making my day

Norman