# hole thru spindle enlargement?



## casca92 (Jul 10, 2017)

once again to the well informed ones
jet lathe BD 920n 9x20 lathe has a 25/32 hole thru spindle*
what are my chance to enlarge to 1"  if I use 4 drill sizes (or more if needed) 
doing it by electric hand drill and level  and rig some type of guide or brace.
then hone the bore.

not sure this is needed at this time, but hey it is 25/32.  if it was easy  I would ask my mom to do it

thanx
casca


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## Alittlerusty (Jul 10, 2017)

If u can't get a bigger lathe to replace that one I would consider buying a used /replacement spindle and beat up on that one.


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## darkzero (Jul 10, 2017)

I doubt anyone could answer your question unless they have the same exact model lathe as you & have inspected the spindle with the same intent in mind.

There's a reason why the spindle bore is the size that it is. If it could be that much larger I'm sure the manufacturer would have. If you just blindly do so, this could be a very expensive mistake.

Proper way is to remove your spindle & take good measuremeants of the OD & ID in all areas that are questionable. Not just where the bearings are either. There could be other areas of the spindle where the wall thickness may be thinner.

You'll also have to determine what minimum wall thickness is safe. Many factors come into play with determining minimum wall thickness that will still have sufficient strength/support.

Not saying that it can't be done, I'm just recommending at the least it would be best to remove your spindle & post up measurements here if you seek the advice of others. I for one am not qualified to give that kind of advice & I certainly wouldn't want to be liable if a failure did occur based on my advice anyway.

Hopefully it may be possible though, please post if you are able to. I'm very curious.


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## Ulma Doctor (Jul 10, 2017)

the boring or the spindle, while seemingly innocent enough, could create a hazardous situation.
if the spindle were to break near the chuck during operation, the dismounted chuck could kill or seriously injure you or a poor bystander .

i'd do a lot of measuring and a lot of research before attempting thinning a spindle of a machine tool
not sayin' it can't be done. but, just because you can doesn't mean you should.


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## 4GSR (Jul 10, 2017)

If it's anything like the spindle on my Rockwell lathe, there are two woodruff keys in different locations, that go pretty deep into the wall of the spindle.  Hate to bore into one of them and it drops into the ID of the spindle.   That's almost a 1/4" of material on the diameter to remove.  I don't recommend it!


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## Buffalo20 (Jul 10, 2017)

even if the spindle was thick enough, boring it out would also ruin the MT taper inside the spindle.


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## darkzero (Jul 10, 2017)

I've said it before & always happy to say it again, listen to the Dr., he knows what he's talking about! 

And if it is possible to enlarge it some (highly doubtful of anything close to 1"), a drill bit is certainly not the way to do it, that's just asking for trouble. And don't even think about using a hand drill, nothing you can do to brace it will make it rigid enough & give good results. Drill bits don't make accurate holes, they just make em. If your spindle bore is not concentric as it is, a drill bit will just follow that hole.

Correct way would be to bore it, & not simply with a unsupported boring bar. You would have to line bore it on another lathe that's capable of doing so. It's probably too much trouble than it's worth but that's just my honest opinion.


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## Ulma Doctor (Jul 10, 2017)

Thanks DZ!

you are 100% correct.
boring would be the op of choice!


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## Ulma Doctor (Jul 10, 2017)

Buffalo20 said:


> even if the spindle was thick enough, boring it out would also ruin the MT taper inside the spindle.


ah, you beat me to it jack!


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## Bob Korves (Jul 10, 2017)

The reason for the 25/32" is for clearance from stock that will go through collets that might fit your lathe.  The next larger common size of collets that I know of is 5C which goes to 1" stock through the collet.  Spindle I.D.'s for 5C collets are around 1-1/2", and you will not be able to achieve that with your lathe.  If it is a gunsmith thing, and you just want to get a bigger barrel through the spindle that is supported by external spider and chuck, or a similar non gunsmithing job, well, you are the test pilot.  Before I would tackle that I would look for a larger lathe...


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## kd4gij (Jul 10, 2017)

I have to agree. Just an all around bad idea.


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## Chipper5783 (Jul 10, 2017)

casca92 said:


> once again to the well informed ones
> jet lathe BD 920n 9x20 lathe has a 25/32 hole thru spindle*
> what are my chance to enlarge to 1"  if I use 4 drill sizes (or more if needed)



?? Well, I suppose the probability of creating a 1" hole in a piece of metal which has a 25/32 hole already in it is about 100% ??  It is just metal and it is not difficult to turn it into chips.

Now if you were to inquire on the wisdom of performing this task, or the Pros/Cons of enlarging the spindle hole another ~1/8" per side - you would get a lot of responses.

The applicability of this change would be very small, even if you could make it work - as others above have pointed out, that is a big IF.
Right now your spindle bore is designed to accept 3/4" stock.  So how often do you need to work longer stock, that is between 3/4" and 1", that you can't fit between centers or support with a steady rest?

A much easier, more successful and satisfying way to get the larger spindle bore is to go buy another lathe!   That 9x20 lathe is a fine enough machine.  If you look after it, then it will always have a role to play.  If your desire is to extend the capabilities of your work shop - buy another lathe.  The 3/4" spindle hole is certainly not the only short coming - if you figure that you want a bigger spindle hole, then you will soon want a little more swing, and I assure you a bit longer bed would be real handy, . . . .  You get my drift, start looking for a larger lathe.


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## 4GSR (Jul 10, 2017)

One quick way to determine if the spindle can be bored out is the look at the tail end of the spindle.  If it's anything like a 9" SBL spindle, it probably has a integral gear cut on the OD of the spindle.  From the root diameter of the gear, subtract a 1/4" from that. (That would leave you with a 1/8" cross section under the gear). Is the result diameter any bigger than the existing ID of the spindle?   If it's larger, go to step two.  Remove the chuck from the front of the spindle.  What is the internal diameter at the face of the spindle?  If it has a No. 3 MT, it's around .94" diameter.  If the diameter calculated at the back end is greater than this, there's a 99% chance it will work.  If the diameter is smaller than .94", don't do it!  Your spindle could come into some where down in the bore.  But remember, this simple test is no way telling you it will work.  There may still be keyways on the OD that could break thru causing issues.  There also may be hidden external under cut areas that are not seen with the headstock assembled.  Take the spindle out and make a drawing in cad of the spindle so you can see the different cross sections and by calculations determine if it can handle the new loads that could be applied to it.


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## 4GSR (Jul 10, 2017)

I haven't bored out a lathe spindle myself.  I have seen larger one' s open up on BIG hollow spindle lathes in my earlier years.  They just needed another 1/2" to get the part to pass thru the spindle.  The hole was already 11".  Guys would rig up special boring bars that had wear pads that kept the bar on center and not let it wander off, causing it to bore a off center hole.   A similar process could be used on a small lathe spindle, too.  I still don't recommend it!


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## kd4gij (Jul 10, 2017)

I thing if it was safe to open up the spindle bore to except 1" stock or even 7/8" stock the manufacture would of done so as it would of been a great selling point. My craftsman atlas 12" lathe will only except 3/4" stock. Besides it doesn't matter how large the spindle bore is. We always wish we had more. We have a lathe with 4" bore and one with a 5" bore and still have to turn down work some times.


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## 4GSR (Jul 10, 2017)

Need a big hole lathe? here's one you could put in your garage. 
	

		
			
		

		
	



It has a 50" swing over the bed with a 16" thru hole on the spindle.  Guessing a 50 HP motor on the back.  Weighs in at about 30K.  16" hole big enough?  Did you say something about making a 14" cannon barrel?


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## casca92 (Jul 11, 2017)

Buffalo20 said:


> even if the spindle was thick enough, boring it out would also ruin the MT taper inside the spindle.


that was 1 I didn't consider


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## darkzero (Jul 12, 2017)

4gsr said:


> Need a big hole lathe? here's one you could put in your garage.
> 
> 
> 
> ...



So...what size MT center does this one take? 

How do you crank the tailstock quill? Do you literally just get up there and stand on the ways?


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## 4GSR (Jul 12, 2017)

darkzero said:


> So...what size MT center does this one take?
> 
> How do you crank the tailstock quill? Do you literally just get up there and stand on the ways?


I think a 16" shell off of the USS Missouri inserted into the spindle.  Might be a sledge hammer fit, be careful of the firing pin. Then machine a 60 degree point on it!
I've been around a couple of these in my past, you can look over the tailstock on your tippy toes.   The tailstock quill screw is on ball bearings with a HD thrust bearing.  It cranks easily.  The real problem is moving the tailstock up and down the ways.  It's missing the bracket for the hand crank that aids in moving the tailstock.  I suspect it wasn't mounted, still in the shipping box.  The tailstock has four spring loaded ball bearings under it that lifts it up off the ways about .015-.030" to make it easy to move by hand, amazingly. 

If this is the lathe I'm thinking of, it just went up on auction in a machinery dealer in Houston that went out of business.  I recall seeing it about 15 years ago at this dealer when I visited them.  This one was built in the mid to late 1980's.  It's way too big for most oilfield work out there, unless you are chasing threads on some casing or doing on offshore sub-surface equipment.  Today, most of this kind of stuff is done on CNC machines, even if they are making one of.  And yes, there are CNC lathes out there with 16" plus bores in the spindle!


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## TRX (Jul 15, 2017)

Take the headstock apart, carefully measure your spindle, reassemble.

Then machine a new spindle with a larger bore, eliminating the taper if needed.


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## GoceKU (Jul 15, 2017)

Sure is possible, but why would you weaken the main spindle, if you need to pass material thru just buy a bigger lathe.


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