MT4 Adapter spun in spindle, how do I clean up the spindle taper?

SLK001 said:
Just a quick question: Is the spindle taper a short taper? I mean, does it have an MT#4 taper slope, but it is only 2-1/2 to 3" deep? A MT#4 has a small end diameter of 1.02", but your bore is only 25mm (or less than 1"). Your spindle taper has to be at least 4.0625" deep to fully engage a standard MT#4 plug. Time to start "fingering" your baby!
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Not sure. Need to measure it. However, if the taper angles match and the taper fully inserts, shouldn't there be a lot of contact? Say one makes a very long taper with a 0.0519" taper per inch and it's 10 inches long, won't the taper engage in the matching section of the spindle? The long taper might be useless, but wouldn't it engage?
 
The manual states the spindle is mt4. The lathe as delivered has a mt4 dead center. I can see that in the parts list. Unfortunately, I'm not the original owner. I either forgot to take it, or it's somewhere in my basement, hiding in plain view! When I picked up the lathe I had a check list, I just found that list. There's pencil marks against most of the parts, but curiously not any of the dead centers I do have one of the mt3 dead centers, but no check mark. Oh well. I could buy a replacement one from Grizzly so at least I have a reference taper.
 
WobblyHand said:
Not sure. Need to measure it. However, if the taper angles match and the taper fully inserts, shouldn't there be a lot of contact? Say one makes a very long taper with a 0.0519" taper per inch and it's 10 inches long, won't the taper engage in the matching section of the spindle? The long taper might be useless, but wouldn't it engage?
Click to expand...

If it is indeed a short taper, then the longer MT#4 adapters will bottom out in the bore (it's too small to fit an MT#4). If it's close, it may "look" like it's properly seated, but instead it just bottomed out. A bottomed out adapter will spin and only make contact at the mouth of the spindle (but not complete contact, so you will beat a line in the adapter right at the mouth).
 
SLK001 said:
If it is indeed a short taper, then the longer MT#4 adapters will bottom out in the bore (it's too small to fit an MT#4). If it's close, it may "look" like it's properly seated, but instead it just bottomed out. A bottomed out adapter will spin and only make contact at the mouth of the spindle (but not complete contact, so you will beat a line in the adapter right at the mouth).
Click to expand...
I hear what you are saying, but honestly don't quite visualize it. I will make a sketch or two to convince myself.
But definitely getting a line in the adapter at the mouth.
 
I just measured the inside of the spindle by the gears. Right now I have a piece in the chuck, that's awkward to move. I get 25.9mm ID at the furthest point from the chuck. If I measure about 50mm towards the chuck, I still measure 25.9mm ID. The small end of a MT4 is 25.908mm (1.0200"). So it's close, really close. Was a quick and dirty measurement with a telescoping gauge and a micrometer.
 
WobblyHand said:
I just measured the inside of the spindle by the gears. Right now I have a piece in the chuck, that's awkward to move. I get 25.9mm ID at the furthest point from the chuck. If I measure about 50mm towards the chuck, I still measure 25.9mm ID. The small end of a MT4 is 25.908mm (1.0200"). So it's close, really close. Was a quick and dirty measurement with a telescoping gauge and a micrometer.
Click to expand...

Yeah, you should really measure from the mouth side for this. The dimension that you need to know is how far in does the MT#4 taper extend? If it extends at least 4.0625", then your problems are elsewhere. If it does not, then your adapters are too long and you need to trim them to match the length of the taper in your spindle.
 
I pulled the work piece from the chuck. Not quite sure how to accurately measure the spindle taper length, but will get an estimate. I'll try a faced 1" rod through the back side of the spindle as a stop.

Precisely trimming the tapers will be fun. At the moment, don't have a good way to hold them. There are no accurate places to grip, besides the taper itself. Guess I would need to make a short MT4 socket. Does the socket need to be made of steel?

Adventures in machining... Making 10 things to do what you originally set out to do. Definitely a pull yourself up by your own bootstraps hobby!
 
Made some measurements. The taper is short in the spindle. But that's ok, since the inside of the spindle seems to be relieved. Distance from spindle nose to edge of normal bore is 4.386". Spindle bore is 26mm, not 25. A 1" rod freely fits. The inner relieved section seems to be 30mm in diameter. I used a 2mm hex to put in the hole against the small ledge as a visual reference. So 26 + (2 x 2mm) is 30mm. If this extra feature wasn't there, no MT4 would fit. The length of the 30mm diameter section is 52.4mm. The taper length is about 59mm. Modeled this in FreeCAD. This is what I see. The gap at the back of the taper to the 26mm spindle bore is 8.28 mm according to my calculations.
Estimated_spindle_fit.jpg
There is some sort of artifact at the mouth of the spindle, or it is interference. I'm not good enough of a CAD jockey to tell. (I eyeballed the placement of the spindle relative to the taper.) I modeled the taper length at 4.060", if the taper is longer, it just protrudes from the spindle mouth, as it will not fit any further into the spindle (if the taper angle is truly 1.4876 degrees). So far, if the taper is true and whatever protrudes into the spindle bore is under 26mm, a real MT4 should fit, shouldn't it?

Guess I should model the actual tang and end of the tapers. I do know in the original adapter, the tang width was 24mm, which will fit in the bore with no problems.
 
SLK001 said:
Just a quick question: Is the spindle taper a short taper? I mean, does it have an MT#4 taper slope, but it is only 2-1/2 to 3" deep? A MT#4 has a small end diameter of 1.02", but your bore is only 25mm (or less than 1"). Your spindle taper has to be at least 4.0625" deep to fully engage a standard MT#4 plug. Time to start "fingering" your baby!
Click to expand...
The spindle bore on the G0602/G0752 is 1.06". I checked the MT4 dead center that came with the lathe and an MT4/MT3 adapter and both agreed within reasonable limits of probable measurement error with the published spec. for MT4 dimensions. Both tapers fit the socket .

I blued up both tapers and checked for fit. The OEM dead center showed contact along the entire length of the taper engagement as did the the MR4 MT3 adapter although curiously enough, there was a suggestion of five lobes on the adapter; probably an artifact of the grinding process.

The length of the socket was about 2.5" and the diameter at the small end about 1.10" , as measure from the wipe pattern on the dead center and with a hole gage.
 
SLK001 said:
If it is indeed a short taper, then the longer MT#4 adapters will bottom out in the bore (it's too small to fit an MT#4). If it's close, it may "look" like it's properly seated, but instead it just bottomed out. A bottomed out adapter will spin and only make contact at the mouth of the spindle (but not complete contact, so you will beat a line in the adapter right at the mouth).
Click to expand...
A longer taper will not bottom out. The bore diameter past the tapered section exceeds the diameter of the taper at that point.
 
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