Grinding Spindle R8 taper on machine. Same for any Bridgeport styled machine.

[Tim9]

I then used some Dykem red again and checked to see how the colllets mated to the spindle taper. Looked okay. FWIW, after I did this I realized that it would be better to use Prussian Blue and not use collets but instead use a known good taper. A solid taper.

I know that it looks like I’m only getting partial contact of the collet, but from the way the spindle was worn before I started, I could see the same wear pattern. Bottom line is that the collets only make contact on the nose... at least that is what I have read from posts on PM.... posts from guys talking sine, cosine and arcan angle crap. Posts in which the person posting this belief of nose contact appears to be very well informed.
So, I’m under the impression that it looks like the grind came out okay. Of course not perfect. And no where as good as sending the spindle out. But better than it was. And I’m pretty sure I could still get it reground once more if need be. So if I screwed it up, I can still send it out.

 

[Tim9]

So next I switched to a finer stone and it’s a smaller stone. It really didn’t appear to do much. No sparks. But I did it anyway. I’m just centering the stone.....making sure it’s centered at least. I put an 1/8” bar in a collet and made sure the stone was center. Just measured it with a ruler.

 

[Tim9]

After the grinding, I turned the spindle speed up as fast as possible and folded over different grades of silicone carbide wet/dry sandpaper. I started with 120 grit....then 220 grit.....then 400 and finally 600 grit. This didn’t take any time since I was just cleaning it up and I never kept pressure in one place. I just pressed with my finger on the sandpaper while the spindle was turning and moving it in and out.

By the way, I did this clean up with the sand paper wet.... spraying with WD-40 first three grits. I had some 600 grit lapping compound.....so put a dab of that on the 600 grit. After that, just a WD-40 clean rag to get all the grit out. Did that about three time to make sure no grit anywhere in the spindle taper. Washed it out pretty good with mineral spirits then....then clean rag...then blown out with air. In others words....get all the grit out. You don’t want any grit messing up your spindle or collets.

After that, I used Prussian Blue this time....and then used a Shars mill cutter R8 taper. I’m happy with the way it looks. Granted, I’m only getting about 75% to 80% taper contact, but I think it’ll be just fine. For one thing, I’m using a Chinese arbor. It’s not like I have a Taft Pearce taper gauge. So there’s no guarantee that my test taper is perfect
And it’s not worth trying to tweak it by adjusting the angle and grinding it more.... Because in my opinion, there’s a finite amount of metal on my spindle. I surely can’t just grind and grind and grind.... tweaking the angle until I get it perfect. I could easily ruin the spindle by taking off too much metal.
Maybe I’m wrong about that opinion. I’m not an expert. I’m not Richard King. But, I’m guessing that as a hobbiest, that this is good enough for government work.

 

[Tim9]

It really looks a lot better and came out pretty good spec wise. I’m getting 1 thousandth using a 1/8” collet and rod....and 3/4 thousandth using a 3/8”

 

[Gaffer]

I'm as rookie as can be at this hobby, but have to say your work looks great. I had to dive into the head of my Bridgeport clone. The forward/rearward tilt didn't work, and I found the key was nowhere to be found. I replaced the spindle bearings too, but now I am hesitant to look into the spindle bore for what I might find. I don't have the skills or confidence yet to handle what you did. Well-done sir.

 

[Lo-Fi]

Great work! Mine was such a mess I had to hard turn it:



I found that the grinding wheel I tried first tended to "follow" the runout regardless of how careful I thought I was being. Runout after turning is sub 0.0002", which I'm pretty happy with. I didn't have a taper I could trust or a sine bar, so had to eyeball it then finesse with dye and a solid shank tool.

Have you found it's made a world of difference to performance?

 

[Tim9]

Thanks Gaffer. It’s definitely not that I’m an expert. But I did spend the first half of my life fixing cars. And this was the 80’s and 90’s. Lots of new brands and pre internet days. So no way to have a shop manual of every model and that kind of just taught me to dive in and do it.
Hell....it was only a broken car. Not like a human life on an operating table. So I just dove in and did it. By and large, I think most anyone could have done what I did. Believe me, I didn’t want to ruin it. Honestly I think grinding is much more forgiving than hard turning. I thought about hard turning like LoFi did. But it was too risky for my skill set. I have some CBN inserts I purchased for a future project of turning my lathe jaws.....and saw a video on PM of hard turning. But I didn’t want to try it yet, especially since I have never used CBN inserts in my life. I didn’t want to experiment on my spindle. I have used a grinder before, so I have that experience. Not a big deal but I went with what I’m comfortable with.

I went with grinding. FWIW, the second stone I tried seems to describe what Lo Fi describes as doing nothing . It just didn’t have any affect in my opinion. But the first stone I used....the white stone easily took off metal. In fact.....I was only able to dress the front 95% of that stone and it was definitely bell shaped the last 1/8” and you can see in the video that it went too far at the end.

I think that’s why my contact isn’t complete in the very front of the blueing on that arbor.
Anyway.....I’m sure I could spend another day on it and get complete contact. But I don’t honestly see the upside since I have pretty good contact of the taper. I’ll play it by ear. And....this project took me more than a week total. The grinder build took me a few days in itself.
LoFi....I honestly just finished it. I only did a small project making a T-nut. I did notice less runout when drilling a 1/8” hole.
My biggest gripe before this repair was when drilling small holes. The bit was just wobbling. That and never being able to use a 1/8” end mill without breaking it. But that may be operator error. And a worn x-axis table. Who knows.
on a side note....when setting-up the mill for the sine bar....I first turned the head 90 degrees. Then for the hell of it....I put the mic in front of the quill instead of underneath it. It turns out my turret wasn’t facing directly forward.
Not sure how that affects stuff. Haven’t given it a lot of thought.....but FWIW....it’s all dead center now.
I’ve been tweaking one thing after another on this mill. First the VFD. Then the bearings. .. and DRO. Then a quill DRO. Then a bent drawbar....so I made a new one. Then fixed wobble of the bent pulley. Then new belt. So all in all....it’s definitely a totally different animal than it was when I purchased it.

I really want to get everything organized and fixed so I can build myself a recumbent bike. That’s what I want to do.