PDA

View Full Version : ? - reaming deep hole



joahmon
10-28-2005, 04:43 PM
I need to ream a .625" dia hole which is 4.5" deep, not blind. The last time I tried something close to this I wasn't happy with the finish. I used a drill chuck in the tailstock of the lathe to hold the reamer and had to move the tail stock to gain the depth. I do not have a drill press with enough travel. Oh yeah, the material is 12L14.

Any suggestions??

Timleech
10-28-2005, 04:47 PM
Would a floating reamer holder help?

Tim

Paul F
10-28-2005, 05:58 PM
What size hole are you starting with? Is teh .625" hole the drilled size or the finish-reamed size?

Are you retracting the tool often and clearing the chips, and using lots of cutting oil?

Also, slow your RPM down to 50-70% of what you'd drill the same size hole at..

This shouldn't be a problem for a through-hole. Blind would be harder.


Paul F.

Rustybolt
10-28-2005, 06:05 PM
Several things may be happening here. The finish on the reamer. Not enough oil to remove chips. Not pulling the drill out enough to to clear chips. leaving too much material to ream and loading the reamer. reaming too slow and loading the reamer. .010 is plenty left to ream better if .005.

Paul F
10-28-2005, 06:19 PM
Having reamed many rifle chambers from .22 or .30 caliber to cases about half and inch in diameter, I can say that as long as everything else is right, .010" is NOT too much to take with a reamer...

But feed, speed, chip clearing, and lube get more important if you're trying to take more than .005" in one bite.

Paul F.

Leigh
10-28-2005, 07:42 PM
A spiral-flute reamer will give you a better finish and clear the chips better than a straight flute, particularly at that depth. Catalog number 3106A46 at McMaster-Carr http://www.mcmaster.com for $30. 2 1/2" flute length, 9" overall length.

------------------
Leigh

[This message has been edited by Leigh (edited 10-28-2005).]

mochinist
10-28-2005, 08:34 PM
The way I like to do a hole like that is first load up the reamer and the hole with lots of heavy cutting oil, next start the lathe for that size reamer I would guesstimate about 50 to 100 rpm depending on what your lathe will do, feed the reamer in about an inch and then stop the lathe, then unlock the tailstock and pull the reamer out, clear the chips from the hole and the reamer and re oil both and then push the reamer back in the hole nice and easy till it bumps the spot where the reamer stopped cutting, next lock the tailstock and back it off about 25 to 50 thou restart the lathe and cut another inch or so, and then repeat the process till finished to depth.

My old master showed me this way, and I always get pretty nice looking reamed holes regardless of material doing it this way.

One other thing it is always best to drill then bore and then ream if you have a boring bar that can handle the job.

joahmon
10-29-2005, 09:38 AM
Thanks for all replies.

Mochinist,
That is the technique I used except I did not stop the lathe before pulling out. Probably the slight cocking of the tailstock caused the poor finish. I'll try your system this time, thanks.

x39
10-29-2005, 05:40 PM
<font face="Verdana, Arial" size="2">Originally posted by mochinist:
feed the reamer in about an inch and then stop the lathe,</font>
That's the method that works for me. The same works well if you're drilling a hole and want a decent looking bore.

Forrest Addy
10-29-2005, 08:20 PM
First drill and bore the starter holea diameter or two deep maybe 1/16" undersize to ensure concentricity. From this you drill through to remove stock.

Rebore to semi-finish size maybe 1/64" under the reamer size. This time the bore is not only to ensure concentricity but roundness at the start. Drill to remove the stock and roughness in the rough drilled hole. You may have to "back off" the drill's cutting edge to a neutral rake.

Now ream using plenty of nasty black cutting oil.

If your tailstock doesn't have enough travel for the reamed depth, tow it with the carriage. Most any lathe can be modified with a towing hitch consisting of aligned tapped holes in the carriage and the tailstock base and a pait of hex head bolt and a link to connect the heads. The trick in this is to have a tailstock that tracks on its ways properly, the right amount of drag on the clamp, and whose quill aligns with the spindle axis.

Peck in about 1 1/2 diameter increments: Mochinist's advice is excellent for avoiding start/stop marks. Chip balls are the bane of reamed holes so don't go too deep with the reamer in one shot. Remember above all that a sharp fresh reamer will produce far better results than one that's clattered in a drawer of tools for years. I'm slack and careless in my shop but my reamers are money makers. I keep them clean, sprayed with a preservative, and store them in the protective tubes they were packaged in.

If you want to ream in two steps and don't have a 0.001" undersized reamer, use thermal expansion to your advantage. Warm the part to 250 degrees right in the chuck with a small torch. Quickly ream it with a reamer you keep cool. Move right along so the reamer doesn't have time to warm and expand into the walls. Allow the work to come to room temp and re-ream taking off the partial thou the expansion gave you.

If you desire a better finish and can afford to go oversized a trifle, split a 9/16" dowel and use wet-or-dry finishing paper wrapped around the dowel to hone out the tool marks. Use a rapid in-out motion: its the axisal motion across the feed marks that best reases them.

If you have a Sunnen hone and a suitable selection of mandrels you can make your bore a nearly perfect cylinder round within millionths and hold a couple 1/10,000 tolerance but that's dreaming for all but the best equipped shops.

Too bad you selected 12L14, it's butter-like softness works against reaming deep holes.

[This message has been edited by Forrest Addy (edited 10-29-2005).]