Thread: Engineered Fits

Originally Posted by new_guy90

do you mean .01mm??? a thousandth reading DTI will move by the slightest change in temperature you are over thinking things remember an on size shaft will not go on the same size shaft working to 0.01 or 0.03 should be fine for most things

do you have formal training of measuring instruments? if not get to know someone who has and get them to teach you i disagree with Dave your measuring should be consistent will all your measuring tools and i mean ALL your measuring tools. to measure bores you can use verniers, telescopic gauges, internal mic's, pin gauges or the very accurate spring dividers im not joking they just as good if not better for most purposes than internal mic's oh and about internal mic's they are a bitch both to use and to calibrate ie an un calibrated mic will give you anything but the size you want the way you get around using un-calibrated internal mic's is to first use it to get your feel in the bore and then use a calibrated external mic to read the internal mic by the way if they are both calibrated right they will read the same measurement now all this is just a PTA if you ask me so my advice is use good old fashioned spring dividers you will learn how to "feel" the true bore size and transfer it to your mic but you can not expect 0.001mm resolution its just to small and a complicated measure to even begin talking about

just to sum up calibrate your external mic you will use to measure the shaft and bore right before you use it and always double check with with a good vernier or hell even a quality rule and remember 0.03, 0.01 is a tight size for a worn lathe

Your going to use the inside fingers of verniers to measure a presision bore or a press fit? they are good for roughing in but thats where it ends.

Dave

Originally Posted by new_guy90

only on quality industrial machinery we have a very worn Takasawa lathe at work but it will still dial in your size every time and you know what its dials are in 0.02 increments why because thats as close as you will need even on a toolroom lathe!!!!!!!!

we also have a russian "S-A-ST-A-C-E" (cant spell it) lathe again beautiful lathe you dial in 2mm and exactly 2mm will come off

Is that 0.02 on diameter or radius? You do know can divide the dial reading up by eye and it is very common to use a micrometer to measure the job directly.

With the other lathe when you dial in 2mm and 2mm exactly comes off, did you measure it when it was hot after the cut or when it cooled down?

Dave

I just slipped out to the shed and did a test cut on a piece of 1214. I turned it down to 0.9202", advanced the cross slide what I thought was 0.005" and cut again. The result was a diameter of 0.9101". This was on my 1969 Hercus.

It would not be hard to have a small misalignment of the calibrations on the collar resulting in a tenth error or more. A dial indicator set up on the cross slide could minimise the error.

David "YarrD", how about some photos of your set up.

In the meantime, here are some photos of Hardinge's indexing cross slide indicator to whet the appetite. I do have Hardinge's spare parts drawing of this attachment. It only shows a plan and section but provides a fairly clear illustration of it's workings.

Bob.

Of course Patrick is right..I meant .01mm. Rush of blood and all that!

As for my DTI set up, I am a bit clunky with photos - I will get my son to help. Set up is pretty basic however. At the back of the Hercus cross slide there are two convenient bolt holes (probably for the taper turning jig). I made up a tray and mounted it to the cross slide using these two bolt holes. The tray thus goes back and forth with the carriage. I put the DTI in the tray, activate the magnet and set the tip touching the cross slide. I can dial up .01mm this way (the smallest division on my DTI). I cannot leave the DTI engaged while cutting unfortunately as it jumps all over the place. So I have to re-set DTI and re-zero it for each cut.

As for cutting, I use HSS. Final cut is at smallest feed plus tiny trailing angle on tool. When cut towards headstock complete, I reverse the cutting direction at same cross slide setting and run tool back to the beginning. In this reverse cut mode and with some nice cutting oil, it takes a delicious gossamer cut with quite good finish. All this on metal from my scrap pile which I presume is mostly rubbish MS.

Thanks for the fascinating dialogue...nice fits are my favourite subject.

David

"Exactly is a big word" Sorry Bob the second one wasnt for you. I'd quote better if the forum wasnt so slow(BTW I find if its really bad I can use poxy servers and it works ok)

Originally Posted by .RC.

I don't really know having never worked in the industry but with CNC lathes they talk about being able to machine to 5 microns repeatedly.

Originally Posted by .RC.

RC I was talking strictly about manual lathes.

Originally Posted by .RC.

I thought about a cylindrical grinder but to be honest I cannot see what it could do that I cannot do on my lathe... I am told that to cylindrically grind successfully you must use coolant and there is heaps of other tricks you need to know to get the best out of it...

I didn't mean to imply that good finishes and extreme accuracy can't be achieved in a lathe. Just that in industry if extreme accuracy and surface finsh was required they would use a grinder.(again talking about manual lathes)



Stuart

Stuart, not being up on computers how do you use a poxy server ?
I agree with you about the surface finish and needing grinding. The surface finish and accuracy on a manual lathe will only get so good, after that it needs grinding.
For most of us home shop guys we have to use emery cloth as our tool post/cylinder grinder which is usually plenty good enough for our jobs.Though I did have to rig up a dremel on the lathe to grind the hardened shaft on my coaxial indicator shaft.

David,
Another thing than can come into play when going for low numbers is how tight your gibs are, they need to be done up with a slight drag and the compound locked if possible.
With getting a nice finish, a tool with a small radius on the end helps out a lot, it smooths out the thread type finish a pointed tool leaves.
I hear some guys on different forums complaining about mild steel being gummy and not getting a good finish, some even say they wont use it at all. I think if you can grind a tool and get a good finish on mild steel you are 3/4 of the way their.

Dave

I'll PM you dave.

I've got a book some where with a project to make your own gauge block(granted its facing rather than turing off the dia). But he claims to be within 0.0025mm I believe, I'll see if I can find it.

Stuart

I got your PM but I couldn't get it to work, not to worry.
Usually this site runs to fast for me, at the the moment it's running slower, now thats saying something,LOL

I turned up a few cylinder squares last year on my lathe only held by the chuck and could not see any difference on my 0.001mm micrometer over 200mm, they didn't need to be any specific diameter just parallel.
That was just after I moved my lathe and hadn't leveled it again, I tried to cut the first one and was wondering what was going on as it was way out and I had made some others a few years before, then realised I hadn't leveled it after the move. I had made up a non critical shaft a few weeks before that and saw it had a slight taper but I didn't think to much about it.

Goes to show how leveling effects a lathe and even though it weighs near 1/2 ton they still twist. It will also affect turning shafts down to small numbers.

Dave

I'll look into it Dave, just for fun. I cant work out why a poxy would work in this case anyway, but it seems to. Its also handy for google books.

Sorry my misstake, not 0.0025mm. On the guage blocks he claims to be able to take cuts of 0.001mm. Settting the compound at 0.6 degree, you get 0.5mm movement from 50mm travel. HSS is a must and of course it has to be honed super sharp.
Even then you would have to sneak up on size unless your cross slide was "exactly" square to the spindle.

Stuart

Originally Posted by Dave J

Your going to use the inside fingers of verniers to measure a presision bore or a press fit? they are good for roughing in but thats where it ends.

Dave

only to double check you are in the same ball park, good verniers will get you with in -+0.03 at but if your measurements with verniers are out by 0.1 or 0.2 then you know one of them is wrong so you should perform both measurements again until you get similar results for example you measure your bore with a telescopic but they have worn flats on the end (very common replace them) you read 54.21mm with an external mic and then double check with digital verniers and they say 54.53mm what measurment will you trust? it is also very common to just read the wrong measurement so even a ruler can be helpfull to make sure you are in the "ball park"

Originally Posted by .RC.

I don't really know having never worked in the industry but with CNC lathes they talk about being able to machine to 5 microns repeatedly.

I thought about a cylindrical grinder but to be honest I cannot see what it could do that I cannot do on my lathe... I am told that to cylindrically grind successfully you must use coolant and there is heaps of other tricks you need to know to get the best out of it...

CNC's yes i have seen some machines hold there size all day while machining 4140 hollow bar into bushes tough stuff i can tell you as for cylindrical grinding i have only watched it being done oh but i do remember the old guy who ran one do some tight sizes less than 0.005mm they are mostly used for surface finish, after heat treatment oh and to keep parts rounder as a lathe will produce more "ovality"

Originally Posted by Dave J

Is that 0.02 on diameter or radius? You do know can divide the dial reading up by eye and it is very common to use a micrometer to measure the job directly.

With the other lathe when you dial in 2mm and 2mm exactly comes off, did you measure it when it was hot after the cut or when it cooled down?

Dave

yes 0.02 on the diameter and yes you can "eye-ball" it accurately its a great lathe... i dont often use coolant on the manuals they are kinda neglected

Originally Posted by YarrD

As for cutting, I use HSS. Final cut is at smallest feed plus tiny trailing angle on tool. When cut towards headstock complete, I reverse the cutting direction at same cross slide setting and run tool back to the beginning. In this reverse cut mode and with some nice cutting oil, it takes a delicious gossamer cut with quite good finish. All this on metal from my scrap pile which I presume is mostly rubbish MS.David

ah this could be why you are cutting undersize when you run the same cut twice you take a spring cut because the tool has practically no load it is free to take that little bit more i think im really not sure the way i think of it is all the slop in the slides and even the flexing of the tool will push the tool a little bit back while under load and i think when you take a tiny cut the tool will wont flex so it takes the difference in flex/slop... all i really know about this is your tool will cut better with a little load on the finishing cut just dont go back over it and it should be fine

thanks Patrick. I will give it a go.

When taking small cuts with carbide you will lose your surface finish, one way to keep it is run the lathe faster and your surface finish will shine like you usually see taking larger cuts and i dont use coolant when machining with carbide, only ever use it to cool the job down to measure when close to size. If you do finishing cuts with hss run it slow with a low feed rate and plenty of coolant and you will achieve a mirror finish.