I blue-d the part to check fit - how do I tell what the results mean?

My Colchester lathe didn't come with the spindle nose bush that allows a center to be mounted in the spindle. I very carefully indicated the compound against the spindle nose, cut the bush, then sandpapered it nice and smooth. To check the fit, I put layout blue on the part as I've read to do, and then shoved it in and popped it out a couple of times.

Now, I can't tell what the results mean. The lathe is old and the spindle nose has a fair number of burrs inside it. I can pretty clearly see those in the blueing, but other than that I'm not seeing much. Here are the pics:



After those were taken, I put it back in and drilled a 1/4" pilot and then a 1" hole (with twist drills) to prepare for boring the MT4 socket. With heavy drilling feed - the bush didn't spin against the spindle nose, which to me says the taper must be grabbing pretty well, as it didn't appear to move at all under some pretty serious twisting pressure from the bit. I can envision though, that theoretically it would still be possible for my taper to be off and the bush is grabbing just the front or just the back of the spindle nose, thus might be able to be forced out of alignment (i.e. pitching its nose up or down) under heavy cutting pressure.

After the drilling operation, the blueing was showing some more rubbing.



Indicating the compound against the spindle nose, I got the error down to .001" in a 1.5" sweep with a bestest DTI before cutting the taper. So, I want to believe it worked out just like I planned and I got a perfectly mated taper - but I'm a rookie at cutting tapers AND reading the blueing for fit, so I'd like some confirmation, or help on what specifically to look for to understand what the blueing is telling me.

lightly turn the part in the taper a few degrees the blue will rub off where it touches .

Bill

You're using the wrong blue Jason you need Engineers Blue like this Engineers Blue Micrometer Blue Marking Tube. | eBay

It's like blue artists oil paint, doesn't dry so rubs off / transfers, TIP;- only use the thinnest of smears what you show with layout blue would be far too thick.

I see you could be ''in the outback'' so to speak and Blue might be hard to get, find some strongly coloured ladies lipstick - does the same job.

layout blue??

You need transfer blue. Also .001" in 1.5" is huge when it comes to tapers. Tenths indicator territory.

Edit- Limy beat me!

DOH! How many blues do I need around here, lol... Ok, thanks for the hint on the lipstick, I'll look some up.

JasonPAtkins said:

DOH! How many blues do I need around here, lol... Ok, thanks for the hint on the lipstick, I'll look some up.

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May I suggest "Slut Red" for the color

iwananew10K said:

layout blue??

You need transfer blue. Also .001" in 1.5" is huge when it comes to tapers. Tenths indicator territory.

Edit- Limy beat me!

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Perhaps when mating a new taper, lol. This one has pitting from age and I'm sure some hits, and the .001 was from running over the non-smooth surface, I think. I was using a .01mm DTI, (so if I'm doing my math right, each tick is 4 tenths), and couldn't get it closer than I did, not because of steady indicator movement (showing I missed the angle) but because it was bouncing a tick back and forth running over the pitted surface.

It sure feels firm when I fit it in the nose, but maybe it would even if it was off.

You could always just make a sholdered piece to fit a chuck and turn a 60* taper on it for a dead center. Just take a light skim cut on it each time you put it in the chuck. The shoulder keeps it from pushing back into the chuck under load.

swatkins said:

May I suggest "Slut Red" for the color

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What Lathe??? He will forget about it when he finds her................

swatkins said:

May I suggest "Slut Red" for the color

Click to expand...

Are we to understand you're an authority on that subject?

Plastigauge

you need Engineers Blue or Prussian Blue: PERMATEX Prussian Blue,Tube,0.75 Fl Oz,Blue - Pipe Sealants - 3DPP9|80038 - Grainger Industrial Supply

Coat one side REAL REAL thin. Keep wiping until you have a even uniform thin coat on one part (the side that is finished). Press and slightly turn the part you are making. A fine blue shine will be seen where ever the two parts make contact. The word is: Very thin and even coating!!
If you overdo it - and most people do - than you have nothing but a big smear.

When I have to match a male taper to a female taper I always relieve the middle third a bit. Then I fiddle around with abrasives of some sort until I have good contact on the front and back areas. If you end up with 50% contact on each of the front and back portions it's infinitely better than if your taper was unrelieved and you had 100% contact on the middle area.

Also, you will want to clean up the bore before fitting if at all possible. What's the taper? I've Cleaned up some very dinged up spindle tapers with commercial reamers with good success. Often on older machines the spindle is soft enough that the reamer will bite off the high spots but hard enough that it would take some serious muscle to affect the whole taper. When proceeding with reaming I use permanent marker on the inner bore surface just to have a visual guide to see what's leaving and what's staying. Otherwise when checking fits it's transfer or 'bearing' blue as mentioned above.

You do need a more sensitive indicator and I agree that .001" on that length is an awful lot of error.

FSH said:

Plastigauge

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Jason,

your OP didn't mention how you cleaned up and prepared the spindle taper before setting the compound.
I would suggest that you use something like 400 - 600 grit emery and polish it to remove anything sticking up inside of the taper.
When indicating the taper it is critical that you also place the dial indicator tip exactly on center for you to achieve an accurate alignment.
Using the contact blue will give you a good sense of the fit overall (the taper contacting over it's length as well as if it makes contact all of the way around the cylinder). Which you sleeve doesn't appear to be doing. Possibly out of round spindle taper.
Using plastigauge will allow you to get an actual number that the angle would be off over it's length if you see any difference in the plastigauge at either end.
When the sleeve fits correctly it will require that you tap it on the small end through the headstock to remove it. I like screw machine's suggestion of relieving the center. That will allow you to concentrate on making contact at both ends to give you the alignment that the taper is for, as well as make removal easier.

I use John's suggestion quite often because it allows me to leave the Chuck in place, take a skin cut on the chucking center, and just use a Chuck jaw to drive the lathe dog when turning between centers.

Limy Sami said:

Are we to understand you're an authority on that subject?

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I also find "Slut Red" fingernail polish to be the perfect material for making center dots on telescope mirrors...

Of course I had to go through a lot of "Sluts" to find one that didn't mind letting me have both their lipstick and fingernail polish to use in the shop!

It was a tough job but someone had to do it...

Out and out expert!

the dye you are using is way to thick
you dont need prussian blue or the likes

clean the dye off the outside and sandpaper it circularly
take a sharpie or the likes of it and draw lines lengthwise half an inch apart
put the bush in the spindle and settle with a deadblow hammer
get the bush out and the places of engagement will be clearly visibile

Here is a sample that shows checking of a taper with prussian blue I had in my collection. Hope it helps you get a better idea of the thickness you need.