View Full Version : Climb or conventional mill for long slots ?

05-23-2009, 06:20 PM
I need to make some parts with a long slot for a sliding member, where the remaining material in the side walls will be around 0.25" wide, 0.187" thick, 3 inches long in mild steel.

With the part held in a mill vise, the side walls are supported only at the ends once the slot is roughed out. Would climb or conventional milling work best in a situation like this?


05-23-2009, 06:37 PM
Conventional milling steel usually gives a better finish, and tends to to pull the material towards the cutter. That being said, I would climb mill each side so that the cutter will push the material towards the vise jaws and hold size better.

05-23-2009, 09:43 PM
You got it backwards, climb milling the cutter pulls into the material, that's why a backlash eliminator is needed. My #4 Cincinnati has the backlash eliminator, when it's engaged the table screw is extremely difficult to turn manually.
If you don't have a backlash eliminator, conventional milling should be used, however you should be able to climb a very light cut, maybe .002 or 3 DOC. It will improve the finish.

05-23-2009, 10:49 PM
Beckley is correct.

05-23-2009, 11:34 PM
When you rough cut a slot, you will be doing both Climb on one side and Conventional the other, finish cuts usually involve small amounts of metal removal and climb will produce the best finish, as was mentioned.


David Powell
05-24-2009, 06:17 AM
If you need to cut an accurate slot of a length which closely approaches or exceeds the length of your vice jaws, in a piece which leaves only minimal support then I suggest that there are two simple set ups which will work. First forget using the vice,simply set the piece up on a sacrificial aluminium plate directly on the bed of the mill clamping at reasonable intervals on both sides. Secondly, especially if your vice is heavy and you are not superman, set the piece up in the vice in the usual way then add parallels ABOVE the work so that they stick up above the jaws about 1/16 , sitting on top of the work in the vice and then arrange clamps to hold the parallels down at each end of each parallel. tighten vice , tighten clamps then Slightly release vice so that the jaws are no longer squeezing the job tight. but are just a guide for parallelism, the load being the vertical pinch provided by the upper parallels. Yes inspector meticulous I know it is probably not the kindest way to use parallels, but it certainly has worked well for me. Climb mill or conventional mill as you wish,or find gives the best results in the material chosen. I hope this helps get straight parallel well finished slots. Regards David Powell.

05-24-2009, 08:00 AM
I ended up taking a 0.003" DOC climb finish cut on both walls of the first piece. It turned out great with finish close to ground in appearance and sides parallel and of uniform width.

If it hadn't come out so fine on the first try, or on tougher material (this is 12L14), I'd probably use one of David's methods or make a fixture for the job.

Thanks guys.


05-24-2009, 09:57 AM
Climb / Conventional Milling Backwards??? I guess, if that is what you want you want to believe, so be it.

05-24-2009, 10:26 AM
I think you're both right but are describing slightly different results/actions. The only thing I disagree with is that the finish would be better conventional cutting.

I think what Keith was saying correctly, is that the climb mill method is pushing the part away from the cutter. I have used that exact method to mill some really thin features in parts. Try turning it around and conventional cutting those same thin features and you will be in for a rude surprise when the mill eats your part.

05-24-2009, 03:34 PM
Here's the final (at least for the slot) result. It's going to be part of a rear tang sight I'm making for a friend's old Stevens rifle. Den


05-24-2009, 04:27 PM
Keep us posted on the sight. Are you using plans? I have a tang sight hovering near the top of my future projects list.

05-24-2009, 06:29 PM
JC, I've examined drawings of a dozen or so older sights including the Stevens. My friend wants elevation and windage adjustments and that has created a bit of a challenge. I'm winging the design based on the digestion of all of the photos. I was planning vertical screw adjustment for the elevation but since the carrier and peep fit so nicely, I decided to leave a twist of the peep as the elevation adjustment method. That, coupled with a side elevation scale, ticked off on the mill, with divisions that give some fractional MOA for this rifle should work ok for now.

I need to tackle the base next and will probably implement windage by having the sight ride on a screw trapped by the base with knurled adjustment knob.

Here are a few of my favorites which I feel fit in with the old Stevens.


What prompted the project was a gunshow price for a Stevens tang of $350 coupled with a desire to hone my machining skills for small, precision work in steel, and a friend whose job was a casualty of the current economy.


05-24-2009, 07:17 PM
i don't know.

if i was faced with that situation ..

maybe I would mill the slot first in a much larger piece.

then put something in the slot to stop it distorting ..when held in vice

and then mill the rest.

climb and conventional ..it will be doing the two at the same time ..not sure weather one cancels the other in a slot ........i would leave the table lock ever so slightly on ..to create some drag ..and plenty of lube .

all the best.mark

05-24-2009, 09:10 PM
Den; Those are all good patterns. Plans for the Soule sights are available at the ASSRA site for a reasonable price, $10.00. I have a set. They can get pricey in a hurry, but nothing else looks right on those guns.

It looks like you are off to a good start.