Accuracy on the lathe

[gus]

"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.

Hi there,

Learned the hard way.The pesky phone rings or the boss wants your immediate attention,you forget to zero in and disaster struck.The scrap bin just got a new contribution.

 

[goldstar31]

No way, Gus. You are adding the obvious tolerances each time- and they add up.
Sorry, but you start at Zero-- and there is only one zero. When the phone rings, when you want a pee, when the boss interferes-- all are different additions to Zero- where you started.

 

[kvom]

One thing to consider is heat expansion. Sometimes the roughing pass will generate enough heat to expand the work beyond the target tolerance. If you let it cool down a bit before measuring for the finish pass(es), you may get a better result.

 

[Tin Falcon]

Goldstar: thanks for the thumbs up. and yes a reference standard is a good idea. if one uses the same instrument to measure inside and outside diameters you are likely good. for example using the tenth mic to measure the od of a piston and the same mic and a T gauge to measure the cylinder you should have a good fit. if you use an inside mic and a os mic compare the two.

I was amazed the fit and finish of the parts from team build one parts from ten shops from all parts of the world came together and fit.


Another point on using standards a buddy of mine worked in a local machine shop. the boss purchased a new mitutoyo multi anvil mic. he did not set it against the standard. he made a batch of parts for a customer only to find all the parts were out of tolerance.
Tin

 

[Teus]

Great tip Shawn very useful. Thm:

I gonna make a same setup, Thanks.

And I just did today. Works perfect for me, thanks again for the tip

 

[Tin Falcon]

When doing precision work know when to take a break and when not to.
when the part is hot from rough cutting is a good time. when you are trying to get the last cut or two in or taking off the last few thou or the last few tenths is not a good time. it is easey to forget whether or not you dialed in for the last bit and if you are working in tenths things can change while you are on break. it does not take much to move the cross slide 1 ten thousands and that is two tenths on the diameter.
I worked in a shop where the tolerances could be plus .0003 - 0.000. a spring pass is all that is needed to take that little bit extra.

Also if you have tolerances use them . on the OD shoot for the high number on the ID shoot for the low one. You can always lapp off a little but add on tools are hard to find and expensive.
Tin

 

[Forestgnome]

Hi there,

Learned the hard way.The pesky phone rings or the boss wants your immediate attention,you forget to zero in and disaster struck.The scrap bin just got a new contribution.

I used to keep notepad in a spring clip screwed to the wall above my lathe for that. Now I have a dry erase board. Best small investment I've made.

 

[dman]

Goldstar: thanks for the thumbs up. and yes a reference standard is a good idea. if one uses the same instrument to measure inside and outside diameters you are likely good. for example using the tenth mic to measure the od of a piston and the same mic and a T gauge to measure the cylinder you should have a good fit. if you use an inside mic and a os mic compare the two.

I was amazed the fit and finish of the parts from team build one parts from ten shops from all parts of the world came together and fit.


Another point on using standards a buddy of mine worked in a local machine shop. the boss purchased a new mitutoyo multi anvil mic. he did not set it against the standard. he made a batch of parts for a customer only to find all the parts were out of tolerance.
Tin

i've never been a big fan of t gauges. i understand the idea of using the same measuring tool to get inside and outside measurements and in a general purpose shop you dont always have an abundance of special indicators but those gauges are kinda sketchy. they rely on force applied to a milled channel to hold two concentric pistons together with friction and some that i have used get wear in the channel and will gravitate to certain dimensions as the rod finds ow spots in the channel. in engine rebuilding shops that are serious about repeatable precision we use dial bore indicators that we calibrate with a 1/10th mic either to an ideal dimension or to the mating part measurment with the same mic.

i do use t gauges in my own garage because i don't have the budget for a lot of inspection equipment. but i do recommend a dial bore gauge to anyone and if the budget allows it sunnen makes some of the best and some come with setup mics to help ensure you get the gauge setup squarely to the mic anvil and spindle to avoid erroneous setup.

if the budget doesn't allow for sunnen gauges my friend uses a cheap dial bore gage that he has replaced the indicator with a 1/10th scale starrett indicator. it works reasonably well.

 

[dalem9]

You can get the 12 inch dig. scale on amazom for 32.99 And the 6 inch for 26.99 DAle

 

[AussieJimG]

I use a micro DRO made from a digital tyre tread depth gauge: http://start-model-engineering.co.uk/category/micro-dro/

It attaches to the lathe (or mill) with magnets.

I need to make some more but at present, one suffices. I just move it around when I need it. It is handy on the lathe and the mill.

Jim

 

[Jeff-in-PA]

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

I have my home shop tools calibrated at work. Since they are "back ups" for my main tools at work ( and only a hour round trip if desperately needed ASAP ), the boss is more than happy to let the inspector calibrate them.

Plus, most dowel pins are made with a +.0002/-0 tolerance. Bot as exactly as a jo block or standard but better than nothing.

 

[Tin Falcon]

in engine rebuilding shops that are serious about repeatable precision we use dial bore indicators that we calibrate with a 1/10th mic either to an ideal dimension or to the mating part measurment with the same mic.

True in the precision grinding shop i worked in we used both dial type and pneumatic comaprators. And I do have those tools available in the home shop . the pneumatic one needs to be set up the dial I got a good deal on, and it reads in tenths. I try to keep in mind the audience here. this is a hobby and many folks are on a budget. so I tend not to focus too much on specialty tools. so folks a dial bore gage or comparator is a viable option but must be set and adjusted with a known reference.

there is nothing wrong with having a gage block set as well. but this is a hobby and if on person is making all the mating parts they just need to fit right . if your "inch " is a few thou big or small it dos not matter. but everything should be compared to one standard.
If you are in manufacturing then you need known accurate references, and if you are involved in a team build things need to be accurate. but to the best of my knowledge there was no true reference when the TB one built there engines and the fit was fantastic. yes I had the cylinder and pistons made in pairs.
Tin

 

[Herbiev]

Aussie Jim I love the tire gage idea. Just got on http://item.mobileweb.ebay.com.au/viewitem?itemId=350580081508&index=3&nav=SEARCH&nid=83357453331
Digital readout for $1.69 so I got two. I also like the idea of aralditing a neo magnet to the tip to give the push/pull readout. I have no ties with this Ebay site. It was the first one I looked at and being a pensioner, the right price too.

 

[Shawn]

And I just did today. Works perfect for me, thanks again for the tip

No problem, glad to help.

 

[gus]

No way, Gus. You are adding the obvious tolerances each time- and they add up.
Sorry, but you start at Zero-- and there is only one zero. When the phone rings, when you want a pee, when the boss interferes-- all are different additions to Zero- where you started.

Hi Goldstar( My Big Bro)

1991 we were assembling and shipping hundreds of Ingersoll-Rnad T-30s out of Singapore plant every month. Tested my Corporate HQ boss's claim he would support me and approve w/o questioning my Capital Expediture Requisitions on new equipment as long as I think it would contribute on margins. Bought the smallest Leblonde 60" between centre Precision Tool Room Lathe so that I could use it during lunch breaks to machine my own stuff. True enough after too many phone calls, the job piece was cut well below critical I.D. Tried machining after office hours but by then Gus was half dead and too many errors. After two more occasions,Gus went home to watch TV.
Have very good precision lathe with "Heidenhahn DRO" and Valenite Carbide Insert Cutters,Mitutoyo Digital Calipers and Mikes and no time and energy to machine.How sad!!!

But we did turn out some very good production equipment and boosted production by 20% with the 8 footer Leblonde and the baby Leblonde along with the full complement of machine tools.

Leblonde Lathe Plant was our neighbour!!!! Never had any problems with same lathe. Gear change was auto hydraulic. Gear box very silent.
But we paid a high price for lathe which was worthwhile.Same lathes ran for 15 years and no problem.

 

[dman]

True in the precision grinding shop i worked in we used both dial type and pneumatic comaprators. And I do have those tools available in the home shop . the pneumatic one needs to be set up the dial I got a good deal on, and it reads in tenths. I try to keep in mind the audience here. this is a hobby and many folks are on a budget. so I tend not to focus too much on specialty tools. so folks a dial bore gage or comparator is a viable option but must be set and adjusted with a known reference.

there is nothing wrong with having a gage block set as well. but this is a hobby and if on person is making all the mating parts they just need to fit right . if your "inch " is a few thou big or small it dos not matter. but everything should be compared to one standard.
If you are in manufacturing then you need known accurate references, and if you are involved in a team build things need to be accurate. but to the best of my knowledge there was no true reference when the TB one built there engines and the fit was fantastic. yes I had the cylinder and pistons made in pairs.
Tin

i've used air gauges in medical manufacturing. they are certainly a specialty item. but a dial bore gauge is in the realm of what a hobbyist could have. i've seen sets for ~$130 and the indicators can be swapped for better ones. you can find deals on ebay if you look. all in all you can have a dial bore gage that reads 1/10ths for less than a 6 pcs 0-6" mic set. ofcoarse you still need the mic to set the indicator. i plan on getting a set soon.

i used t-gauges in the airforce alot and still do but i don't like them. if it's what you have then work with them, they are certainly better than calipers. but there are certainly alternatives and condition is everything.

 

[goldstar31]

Hi Gus,
I was also having a happy thought and it has just dawned on me that I have not worked or should I correct that to- never had to work for the last 28 years.

With advancing age and possible threats of serious malfunctions, I'm merely keeping the grey matter fit with gentle stimulation. Hope that I haven't upset you.

Meantime, enjoy your fishing in 2013.

Norm

 

[Tin Falcon]

D: there are many options and choices for measuring tools. And what tools are purchased and go in the tool box are a matter of choice.
What I consider production tools may differ from others opinion. Things like geometric die heads , tapping heads , turret tail stocks turret heads for cutting tools etc. even cnc tools are item s that can show up in a hobby shop but were originally more designed for production. Once a guy gets some experience here he will know what to buy and if it is a good value for him or in some cases her. we do have some women. IF someone is building multicylinder engines with many copies of the same part these tolls are valuable.
I admit I have some of the more advanced more expensive tools the die head and tapping head I purchased used and I built my cnc. I have a teclock /tachachino seiki tenth bore gage I picked up used.

I guess what I am trying to say is to say is;
1) machining is adaptive and creative .
2) asks 8 machinist how to make a simple part expect ten different answers
3) this is a hobby for fun. The people will choose what they like and works for them. .What they can afford.
4) I try ti keep it simple for the beginners we get a lot of folks starting with no tools no experience. I do not want to overwhelm Them with a long expensive tool list.
so it is all good.
Tin

 

[gus]

Hi Gus,
I was also having a happy thought and it has just dawned on me that I have not worked or should I correct that to- never had to work for the last 28 years.

With advancing age and possible threats of serious malfunctions, I'm merely keeping the grey matter fit with gentle stimulation. Hope that I haven't upset you.

Meantime, enjoy your fishing in 2013.

Norm

Hi Big Bro.
No offence taken. We are good friends on HMEM.It took me a long time to get used to retiring completely at 58. Today at 69, Gus is expert at retiring with 1001 hobbies.Boating,local,
faraway fishing,aeromodeling,rod building and model engine building.All these hobbies can be cheap if you make it cheap but I go for quality instruments.Grew up and old with Starret,Mitutoyo etc.Bought some Indian Try Squares.They fare better over the chinese made.The Chinese Dial Gage turned OUT OK when first I used it last week.The Chinese Height Gage I bought came with a cheap n nasty box unlike the UK made with a very good strong box.Will DIY my own with USA plywood and post it to rub in the fun.

Merry Christmas.Keep busy. Take care.
Plan to stay on with engine building at 82 & above.

 

[GWRdriver]

I try to keep in mind the audience here. this is a hobby

I think this is very important. For all the usual reasons some us enjoy a greater wealth of tools than others and we can lose sight of how daunting that could be to some, and we don't want to discourage anyone. I can recall when I viewed even a simple DTI as a luxury which I might enjoy, . . maybe . . someday. I still haven't gone very far beyond that. My first mentor (40+ years in tool & die) allowed himself only an ancient Starrett #564 "Junior" indicator in his home workshop. He wasn't a cheapskate or denying himself, or a Luddite, he just didn't need anything more elaborate to do his usual spectacular work.