[photomankc]

Trying to make some TTS type holders at home on the lathe and things were going well until I tried the reamers out for makinig the shank hole. I checked and dialed in the tailstock but it's 0.0015 high and I can do nothing to adjust that out. Figured that would result in a somewhat oversize hole. I actually get a well sized hole from the reamer. 3/8" endmills pop when they pull out and act like a piston going in so you can feel the air pushing back.

Problem is the holes runout is bad. It's right at 0.0015". Not at all what I was hoping to achieve. I can not understand how I can have runout in the hole after drilling/reaming? I can see it being oversize, bell mouth, all kinds of other stuff but how the hell can it be off center from the rotation axis of the damned lathe?

I wonder if I would be better off to make the holes in the mill?

[cornbinder23]

Are you checking the runout on the lathe after the reaming operation or on the mill after installation?

Could be runout of the spindle/collet, or possibly contaminants in the taper of the spindle

Adjusting the tailstock lower would require shimming the back of it up which is what I had to do with mine, as the mating surface was out, I chucked a peice of ground .375 bar in the tailstock and found it to be angled up at the nose a bit so shimming the back up brought it parallel with the spindle

JTCUSTOMS

[photomankc]

Yeah I was checking in the lathe with nothing moved. I'm using scrap until I have something that works because O1 drill rod at 1.5" diameter is not cheap and I don't want to scrap the holders I have that are all done profile-wise.

I was thinking I might be better off to drill/ream them in the mill spindle instead, but getting centered over the drill and reamer will be a time-consuming operation.

[hoss2006]

You can't trust a drill to drill the hole perfectly concentric no matter how true the tailstock is.
Drill to remove a majority of stock then bore the hole to .010 undersize, the ream will track into that hole much better.
Hoss

[Jay Roy]

I would do what hoss2006 suggested, or if possible, just bore it right to size...

[photomankc]

LOL, man. I have a little indexable boring bar that can handle a minimum bore of 0.250" on the way but I'll have to make a holder for the 4-way for it. Tool to make a tool to make a tool. Good times. I better use the reamer though. The indexable boring bars I have do not leave a nice smooth surface in steel especially when you try to sneak up to spot on size.

[hoss2006]

The 3/4 bore holders I made I bored to size since I didn't have a reamer.
I made a few 3/8 too just boring them but the reamer was easier and more accurate.
If you blow over a 3/8 by .001 it's crap but then you can make it a 1/2 holder, I have a few of them.
The 3/16 and 1/8 holders had to be drilled and reamed so it's a crap shoot,
I started with the small ones and any that weren't acceptable for runout were changed to a larger diameter.
Hoss

[mc_n_g]

Read and heed what hoss2006 said about drills and reamers. If the drill wanders the reamer wanders. Period. End of story.
Buy some small carbide boring bars from MIcro100 to create a straight hole first. If you are afraid to bore the hole to size, bore undersize and then run a reamer through the bored hole.

[cornbinder23]

also are you using a center drill for starting a pilot hole?

JTCUSTOMS

[hoss2006]

I assumed you use a spotdrill whenever drilling a hole, it's machine shop 101.
Still no guarantee of the drill tracking true but helps and it's just something that you always do.
Hoss

[DSIF]

Bore for position,ream for size.

[photomankc]

Yes. I use a spot drill when I am not drilling for a tailstock center. When my small boring bar gets here I'll try that. Problem is that it's a 0.250 minimum bore so anything below a 5/16 holder is going to be drilled. I guess that's really getting down to the minimum recommended size for a set screw holder anyway.

[photomankc]

Well, I think I am just going to shoot for boring them. I bored the holes to approx 0.010" under and then ran the reamer. Similar result. I'm getting over a thou of runout, although one of the two I tried is actually usable at a bit under a thou.

I measured the bores just before I ran the reamer and they were concentric. I measured after I ran it and same story seemed concentric but the end mills have wiggle room. I'm going to try the undersize reamer to see if that takes it up but first I'm going to have a go with just boring it out. The tinsy tiny insert boring bar is really pushing it trying to reach out 1.250 though. I have to run at 520 RPM, any more than that and it sings.

I don't seem to be able to get a good reading with the little telescoping gauge for 3/8" holes either. It keeps telling me I'm getting .3748 pegs into .3725 holes. I know that isn't happening so something must be up with that tiny gauge. I can use it to get close but then I'm going to have to run a pass and check, rinse, repeat.

[hoss2006]

This reamer guide could give you some tips.
Reamers Guide
It's possible your tailstock could be off a tad enough to blow the hole over.
From experience, the amount of oil you use can change the final reamed hole diameter too.
A small bore mike can give you an accurate measurement if you want to go the boring route.
I have a list of small bore measuring tools under accessories on the site.
g0704.com
A runout of .001 on the endmill shank should be considered acceptable for a tool like the TTS that's using a setscrew
to hold the endmill.
It's forcing it to one side so it's not going to be held dead center.
You don't want them too tight or they get to be a real b*tch to remove sometimes.
Hoss

[UUU]

It's very hard to measure these holes. I'd turn up a test guage with three diameters (under, on-size, over) and try this in the hole between boring cuts.

[photomankc]

Thanks for the links. The dial indicator bore gauge looks interesting.

I think I'll just use the end mill shanks as the on-size gauge but the under and over-size plugs sounds like a good idea to start-off.

I would consider a thou or under to be passable. I really would prefer between half and one. One idea I might toy with on the small diameter cutters is to leave all the critical work on the external diameters until after the bore is complete and the set-screw is in place. Then dial-in off the end mill/gage and finish the rest of the tool. That would seem to me to make it possible to get run-out into the low tenths and not have to obsess over the bore or risk making it too difficult to remove and insert the cutting tool.

[photomankc]

LOL......

The lathe can make me feel like such a dope. I went to it with the mini boring bar and using my 3/8" shank 1/4" cutter as the on-size gauge and it MICed at just under .3750 by a couple tenths. I found my spot drill is actually 0.3742" so I used it as my early warning (this might have been seen as a warning if I were thinking about it). The results were great. The end mill just wiggles in and the runout on it neutral in the bore is almost nill less than 5 tenths.

Except.... it's apparently the largest 3/8" shank tool in the whole collection So any other tool is going to show a good deal more. I see them qoute runouts of like 4 tenths on some end mill holders but I guess that is not all that telling because the endmills vary enough that I can't see how you could be big enough to accomdate the largest and hold those great runout numbers on the slightly smaller ones.

I guess I may have to calibrate my happines to holding around 1 thou since that may represent about the best it's going to get with the realities of it all the rest seems to be picking fly specks out of pepper.

Anyway, the boring bar works and I think I will just stick to it. Just hate the white knuckles towards the end when you are trying to shave a few tenths and try again.

Thanks for all the tips and suggestions. Close-fit boting is just such a treat!

[JCMills]

Drill, then bore at least some distance--does not say how deep it is. use stout carbide short boring bar and let it springcut the first part of the hole. Even if quickly swapping to a finer sharper boring tool sharpened almost to a point--spring bore that first part. use carbide reamers which are cost effective. ream hole with heavy coolant--not oil.. Holes will ream oversize because the heat expands hole inward onto reamer.Squirting in small amount of lube into hole will not hurt--but use coolant..Ream hole with slow feed ignoring cutting speed and high rpm for carbide reamer. Correct situation of tailstock not being right. Boring to size is not cost effective in most cases. Consider spinning relief on back part of reamer..