[bowentw]

Have been attempting to drill a no-slip fit hole in aluminum using a undersized drill followed by a reamer. Have noted that the hole is not consistently sized and looks to be bell mouthed at the end closest to the drill chuck and tight at the exit in the back. There are three distinct possibilities:1) the tailstock is misaligned; 2) the chuck is not seated in the tailstock assembly correctly; 3) the drill chuck itself lacks precision and misaligns the drill. Would appreciate any help in the identification and resolution of these errors. Will make the tailstock alignment bar in the future; however, this solution does not address items 2 and 3.

Thanks

[vulcom1]

Not sure if I can help but with my old Atlas if I am boring a tight hole I use a short countersink to start. Either that or use a sharp cutter on center on the end for a place for the drill bit to start. Mine won't drill that straight to start with a long bit as there is play but doing this before hand gets me going straighter. I also like to run in a boring bar to bring it out to specs if I have the room.
John

[Dan S]

bowentw,

what lathe are you performing this operation on, also what is the diameter, and depth of the hole?

[pastera]

On the minilathe, you can add headstock alignment to the list.
You will first need to align the headstock to the ways - mine was out 0.015 @ 10" when I got it. A DTI is needed to get any real accuracy.
http://www.gadgetbuilder.com/Lathe_Align.html

The tailstock is most probably going to be high - you can take care of this at the headstock but will need to do fore-aft aligment of the tailstock.

As far as the drill, check the grind and use a center drill to start.

Aaron

[bowentw]

Aaron,
I have a green 7x10 minilathe. Your article on angular alignment and height alignment was quite informative. Will put my DTI on the drill rod in the tailstock chuck and repeat your technique. Like you pointed out my drill makes a scrapey sound when pulling it out of the hole and reinserting it. Probably because it is scraping the side of the hole. Right now I am drilling 3/8" thru-holes in 1"diameter 6061 aluminum as test cases prior to making my final part out of steel. Have checked the chuck runout with a drill rod and it seems to be about .001". Will check the tailstock alignments this evening and let you know how it comes out.
Tom

[RICHARD ZASTROW]

One old trick is to bore the first 1 1/2 - 2 dia. deep followed by the reamer. This eliminates the need for a longer boring bar and the short bored hole acts to guide the reamer straight down the center. You could also try a gun type reamer. The guide pads seem to keep it in line & hold size very well.
They also burnish the id to improve finish.

[pastera]

Tom

That's not my site, it's the one I used to align my lathe (7x12).
If your drill is making noise on entry/exit, it's not aligned. But this is only half the issue, the headstock is more important.

After aligning my head stock, I can turn with no taper over 4-6" as measured with a good quality micrometer. By changing headstock alignment, the tailstock is automatically off, so you need to do the headstock first. A good shim material is regular aluminum foil. Also, if you can, use a torque wrench to tighten the bolts so you can get things to repeat.

Aaron

[widgitmaster]

A Dial Indicator with .0005" or .0001" accuracy is the most handy tool! With it you can test the concentricity of the spindle bore to the tailstock bore, as well as the parallism of the spindle to the ways.

I agree with all I have read in this post, and suggest you first dial the headstock true to the ways, then dial the tailstock to the headstock! If the tailstock has worn, and is below center of the spindle, just turn the drill flutes horizontal prior to drilling! But this does not help with a rigid reamer. For those, simply hold them short (close to the end) and let them find center on their own as you feed them in slowly!

Another good trick is to make a block with a setscrew that mounts on the compound, then drill and bore a hole in it using a boring head mounted in the spindle. this ensures the bore is perfectly aligned to the the spindle, and every drilled hole will be perfect!

Hope this helps!
Eric

[bowentw]

Aaron, Eric,
Measured the headstock height with a 3/8" drill rod and the tailstock with 3/8" drill rod and found that the tailstock is about .01" higher. Therefore I will have to remove the headstock and insert some shims to bring it up to the same height. Any recommendations you might want to share prior to my delving into the removal and shimming of my headstock?
Tom

[Runner4404spd]

take the tailstock appart at the joint and make sure that its not all full of paint throwing off your readings. also be careful shimming the headstock as you don't want to make it not parallel to the bed.

[pastera]

Clean up the tailstock but don't remove metal unless it is absolutely necessary.

The headstock mounts to the ways at three points, two on the prism and one on the flat. Placing shims on either side of the prism at the front/back of the headstock will align the spindle with the ways. A shim on the flat will move the spindle up and toward the front. This is the best way to adjust tailstock height.

It is also better to indicate the tailstock taper rather than rely on the drill chuck accuracy.

Aaron

[RotarySMP]

The Mini Lathe Tailstock is a real POS!!!

Here is my write up of improving my Lathe.

http://www.wrathall.com/Interests/ma...ent_check1.htm

[bowentw]

Disassembled the tailstock and cleaned out the rust and nicks between the pieces and reduced the tailstock - chuck height difference to somewhere between .0015 and 0030 inches. Still have to measure the alignment of the chuck to the ways with some 1/2" precision ground rod. Adjustments to align the chuck may reduce the height difference even more. Will keep you posted.

[vulcom1]

If you are that close I would be measuring with a good centre in the tailstock. A drill chuck is not the most accurate and I think after you take one measurement take it out and rotate it and do it again. I don't think they will be the same.
John