Correct order of machining steps

My advice is: There are a lot more fun things to do with small lathes and mills than trying to make RF connectors. But since you already have a vector voltmeter (Z 'meter) play around with various set-ups and meter the results for minimum vswr, i.e., correct impedance. You will find the proper set-up in the process. As for me, I think you'd be better off purchasing the adapter and spending the time saved on other machining projects.

Bob (knows a little RF) Swinney

So the questions are; Should I start on the inside or outside?

For getting the I.D. exact, should I step drill up, and finish off with a boring bar, or should I find a adjustable ream to finish?

For reference I have access to a Sherline lathe and mill, 3 & 4 jaw chucks, compound cross slide, rotary table, and adjustable angle plate. I've done basic operations on both the lathe and mill, but mostly in delrin and other plastics.

All advice is appreciated.

Robert

...

...

If I had to meet this requirement, I never would make anything.

My suggestion. Ruff lathe OD and ID. Cut your slits on mill. You can skip lathe ruffing if its not helping to cut the slits more easily.

Put part back in lathe, finish turn OD. Bore ID, part off. If you have trouble getting ID tolerance, you'll have to ream after boring. It might work just fine to make a "D" bit reamer.

Plan a few "pracitce" parts. Brass can want to hog in on ya. 0 rake angle helps this.

Have fun.

karl

Cut the slits and then turn OD and then bore? That calls for troubles. It will look like a tulip. :-)

Finish part in the lathe (except cutting off), cut slits on the mill and part off in the lathe (or mill). Pay attention on how you cut the slits on the mill. Best is, that the blade is pulling in the axial direction as much as possible. A sharp thin HSS blade with well over 1000 RpM (at 55 mm diameter) will work.

Nick

Follow good machining practice----rough the exterior and interior, then finish each of them. Cut the slots last-----you'll have no end to trouble if you don't. Regardless of what the part does once slit, the diameters will remain constant to one another and will still be functional. As Nick alluded, make sure the slitting saw is pushing the part away (conventional milling, not climb milling) to avoid a disaster.

Harold

Just in case you only want the parts and aren't focused on machining from the solid, have you considered soldering these things up from "telescoping" brass tubing? Go to a well supplied hobby shop to get it. I buy it in 10" or 12" lengths. It comes in 0.027" wall thickness and is sold by the 32nd of an inch of OD, so there is about a 5 thou "slip fit". Works real well.

Pete Stanaitis

--------------------

SignalFerret wrote:

To be more precise, I'd first rough the outside, then rough and finish the inside. Because brass can be a real bitch when reaming, you want wall-thickness. So when roughing the outside, leave enough material.

I meant that the cutting forces have to stretch the part. Second, I would start cutting from the end towards the center. This results in climb "milling". When working with delicate parts with the slitting saw or a milling bit in the mill, often a climbing cut is much better. The cutting forces are so small, they won't move the table at all. Also, a climb cut doesn't start with rubbing, but with cutting. So the part will bend less.

Nick

Heh!

Just when i finally start thinking you're good for something besides complaining about OT posts, you have to screw up and post the above nonsense. If you worked in my shop, you'd be fired for that one, Nick.

And you've done this on thin parts without problems? That you're using a thin blade makes no difference when you have a thin cross section that is easily flexed. Table movement isn't a concern, but that doesn't eliminate the flexing of the part, and that is a the problem. I've done more than my share of such cuts, and don't agree, not at all.

I, too, cut from the outside, but anyone that desires no trouble will ALWAYS conventional mills such a part. If the rubbing (and bending) you speak of is of concern, climb milling is a sure disaster. You need not be on the *wrong* side of center, so you don't climb mill. You lose big time on this one, Nick.

Reason?

If, and there's more than a good chance it will, the cutter, in the process of climb milling, hangs up the slightest amount, the part flexes into the cutter, either breaking the blade, or screwing up the part. Smart people don't climb mill with slotting saws. There are other ways to feed the blade without risk. If I didn't learn anything else in my 50 years in the shop, I learned that.

Harold

For what one? Maybe it's climb milling that I confused (but then you should have realized that with my comment about rubbing):

+s --> path of tool +------------ | work +------------- +s is the axis of the slitting saw, rotating CW. Path of saw is to the right. Cutting forces will bend the work away (downwards) from the saw and not pull it into. They will also stretch the work. If you would start in the middle and saw outwards (disregarding the fact that the part is too small or you being the only one having such a small blade), you would weaken the part and it will get less and less stiff on the side where you still have to cut.

Now is that climb milling? My dictionary doesn't list it. But google. It *is* climb milling. And if you try to tell me that you would like to let rotate the saw CCW in the above setup, you make me **really** laugh! Or did you have one beer too many?

Nick

Terminology is screwing us up, I'm thinking.

I'm assuming the cut would begin on the left side in the illustration above. If so, yep, we're saying the same thing. Fact is, it's still climb milling to some degree, and can't be avoided unless you run the saw to depth first, then feed across the part. That's the ideal way to make a cut like we're discussing. The cut must be on the centerline, and on both sides, it goes without saying.

OK---I just re-hired you, Nick. :-)

All depends on the direction of rotation of he saw in that example, or the side of the part you choose to machine. It can be both--climb milling or conventional. Machining in that fashion could yield trouble, as you allude. It's important that cutting force is always pushing the part away from the cutter, never in towards the cutter. Because of the geometry of setups of this type, you often are, in fact, climb milling, at least to some degree. I now realize it's more important to discuss how the tool sees the part, not so much whether you're climb milling or not.

As I've already stated, it's hard to avoid climb milling of sorts with slotting saws----but your comment of running the cutter CCW is exactly what I was referencing. That, indeed, would be a mistake.

Too many beers? Not a chance. :-) You can count on two hands the number of beers I've consumed in the past several years. Talk about glasses of wine, or scotch and water, that's a whole different story! :-)

Harold

Thanks, boss! :-))

Absolutely no doubt!

ACK! But it is not avoiding climb milling, but using it. I'm talking about delicate cuts, not heavy cuts on rigid parts with a big thick blade.

Nick