[SCzEngrgGroup]

I needed M22 LH, too.


Thread Milling Slideshow by neilw20_2008 | Photobucket

The advantage of the solid threadmill I got is it has four flutes, so will cut up to 4X as fast (which is still slow....). I do like the idea of replaceable inserts, however.

What kind of feedrate can you run with that?

Regards,
Ray L.

[neilw20]

Hi Ray,

Cant actually remember feedrate. I just push it till it sounds nice.
If it had a carbide shaft it would be much stiffer. I think I took 3 cuts plus a spring pass.
Absolutely precise thread.

I only had a few to do. My lathe does not think metric (yet)
Standard inserts -- yes. Can do whitworth too.

I can email you geometry if you wish. Just touch tool on grinder to give more front clearance.
Took forever to cut that pocket. Who cares. Just hit the start button.

The screw hole is 0.004" to far back, intentionally, so that the insert pulls back tightly into the recess.

Neil

[newman55598]

Ray. What speeds and feeds are you running with your thread mill?

[SCzEngrgGroup]

Ray. What speeds and feeds are you running with your thread mill?

Not pushing it at all right now - 6000RPM, 18IPM linear feed, which is about 8IPM on the helical path, doing about 0.015" DOC per pass.

Regards,
Ray L.

[newman55598]

I had a bench top mill with a max spindle of 1680 I was running f3.36 @ 1680 rpm with a doc of .050 four flute .3720 carbide thread mill.

[AUSTINMACHINING]

The first threadmill I bought was a single point 4_40. My first thought was "no way this could work". The flutes are hardy visible. It made beautiful threads. How they can grind something that tiny is amazing.

[kvom]

Neil,

What's the descriptor for the insert and where did you get them?

[neilw20]

60° and 55°
Valenite Grade:VC905 is the ones I have.
16 IR AG 60
16 IR AG 55

[keithmcelhinney]

Hey Ray got a question for you. Using the fixture, do you bolt the parts down and cut them out, tab them, or flip them over and machine the bottom off? On my machine now I bolt each piece down but once I get the Pro and can cut a bunch at once it is going to take a good amount of time to bolt each piece down...

Thanks - Keith

[SCzEngrgGroup]

Keith,

It varies, depending on the part, but most often I have some kind of clamp for holding the raw "blank". I then drill holes for screws, install the screws, and remove the clamps, then do the bulk of the machining. Using a power screwdriver, it doesn't take long to do the screws. If I were doing higher volume, I'd do a pallet setup that would allow me to do the screws off-line, and just swap in a whole pallet of pre-screwed parts, to minimize machine down-time. But in the small volumes I'm doing, it's just not worth the extra fixture cost.

Regards,
Ray L.

[keithmcelhinney]

Thanks Ray! I do 90% of my machining on fixtures and that is what I do. I think I am going to set up a base fixture and have all of my other fixtures attach to it so I can square and zero the base fixture and have all my real fixtures indexable to the base so I can save zeroing and squaring every time I change fixtures. I actually pinned my table on my 135 and it save a ton of time but there is no way I am drilling holes in my new table .

-Keith

[SCzEngrgGroup]

There are good days, and then there are days like today..... The PDB contains four stand-offs - 1/4" brass tubes, threaded #10-24 on both ends. I had expected to spend a few hours this morning making 20 sets of these. Instead, it took the entire day!

The tubes I ordered seem to be surprisingly hard, and it proved near impossible to cut threads using a standard tap. So, I had to resort to drilling the tubes to a larger ID, and using a thread-forming tap. This required building something to hold the tubes, so I took a 4" 3-jaw lathe chuck, and bolted it to a 4" x 4" plate, so I could mount the chuck in my milling vise. I then hand-wrote G-code to drill and tap the tube. While time-consuming (10 seconds of chucking a part in the lathe chuck for every 10 seconds of machining), it did work. Well, up to a point.... I discovered about half-way through that the tap had apparently worn enough that I could no longer screw a #10-24 screw into the freshly cut threads! I had only the one thread-forming tap (the other having succumbed to an unfortunate accident), so I went ahead and finished them all, and, once done, had to manually "chase" the threads with a spiral-point cutting tap to cut the threads to full depth. Funny thing is, the thread-forming tap still looks like new, with even the coating completely intact! Very odd!

This was my first time using a thread-forming tap, and I do like them, though it seems this brass was not the best material to use. A thread-forming tap is definitely much stronger than a spiral point tap, and makes a very clean, smooth, thread, with no chips or strings. On more ductile material, I expect they work really well. I will be trying them out on aluminum first chance I get. I do suggest doing a few manual "test runs" to get the hole size correct being diving into power tapping. I think in 6061, they should work really well.

Also refined by tapping head G-code - I found that doing a rapid for the retract at the bottom of the hole makes for a rather abrupt reversal. I instead now do the retract at 3X the feed speed, then slow to 2X once the reverse clutch has engaged. This seems to work better. I also learned you want to have a short dwell after extracting the tap from the hole or retract well above the hole. I mentioned above I broke one of the two thread-forming taps I had. Since the part was being held in a 3-jaw chuck, which was held in a 6" vise, with the tapping head in the spindle, there was only about 5/16" clearance between the end of the tap and the top of the part when the head was fully up. I wrote the G-code to retract to 1/4" above the part, then do a rapid back to 0,0. Unfortunately, with so little Z clearance, the tap had not quite fully backed out of the hole before the rapid, breaking the tap. I added a 1/2-second dwell between the retract and the rapid, to make sure the tap was fully out.

First true "production" PDBs will ship out next week! I got all the anodized parts back yesterday, and they are absolutely gorgeous - even better than the batch I did for the beta units!

Regards,
Ray L.

[LeeWay]

I had some of that hard brass tube a while back.
I needed to increase the ID some. It did not like it. It worked, but not without a lot of fuss. Definitely not free machining type stuff.
I just turn everything out of brass rod now. Much nicer.

[kvom]

You might try annealing the brass before tapping. Or use aluminum for the standoffs.

[SCzEngrgGroup]

I had some of that hard brass tube a while back.
I needed to increase the ID some. It did not like it. It worked, but not without a lot of fuss. Definitely not free machining type stuff.
I just turn everything out of brass rod now. Much nicer.

Lee,

Do you know a specific brass alloy that machines well? The stuff I got is apparently 260, but I don't know anything about the properties of brass alloys.

I am going to try aluminum rod next time as well, though I've found these to sometimes be difficult to make in aluminum as well. But I would expect the thread-forming taps to work very well in 6061.

Regards,
Ray L.

[LeeWay]

This is where I buy all my brass rod.
Best prices I could find anywhere, but I buy alot.
4 rods of both sizes I use at a time and I try to wait to get free shipping and sometimes 20% off.
These are free machining 360.
They cut like butter.


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I have only used a couple form taps and never really liked them too much for regular tapping. I think they would work best in thinner material. Like sheet metals. 11 and 12 gage. That is where I used them before. They seem to add more threads than a standard tap to thin stuff.

[SCzEngrgGroup]

Without a discount, OnlineMetals is cheaper for that - $9.86 for 8 feet. I'll give it a try.

Regards,
Ray L.

[rlockwood]

Why not just use an off the shelf standoff? Granted, #10-24 probably isnt readily available, but a fastener change to #10-32 should be simple enough.. then you're paying a few pennies for a completed piece, certainly your time is worth something here..?

[LeeWay]

Okay.
For instance, my regular bushings that I can get off the shelf are 3/8" OD x 1/4" ID and 5/8" long.
I cannot use steel because of rusting. SS was too expensive. 863 bronze at Mcmaster are .66 cents each.

I can make two of these on my lathe in 360 brass in about 30 seconds. I use 40 to 50 of this particular bushing a week.
That is about $33 plus shipping for bronze bushings.

At most $9.00 for material and an hours time in solid brass.

Multiply that by 50 times a year and the savings is considerable.

Granted Ray may not be needing nearly that kind of volume.
Before I built my current lathe, I did buy these bronze ones.

That one, BTW is the only bushing out of 20 types that I can even buy or that come as a standard part. The rest are all specific to my guards and certain saw brackets.

FWIW, when I first started, I turned all these things by hand on a 7/12. I don't miss those days a bit.

[SCzEngrgGroup]

Why not just use an off the shelf standoff? Granted, #10-24 probably isnt readily available, but a fastener change to #10-32 should be simple enough.. then you're paying a few pennies for a completed piece, certainly your time is worth something here..?

Off the shelf ones are not available in the required lengths, and are stupid-expensive in the next longer size.

Regards,
Ray L.