Threading

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KellyJones
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Threading

Post by KellyJones » Sun Jun 23, 2019 6:34 pm

Thought I would share an experience I had this week. I am by no means an expert in machining. Although I've had my Grizzly G4003 lathe for almost 15 years, I am still very much a newbie. For instance, I have only threaded on my machine one time before this week.

Earlier this spring, while readying the lawn mower for the season, I broke an 18" breaker bar trying to remove the nut holding the blade on. (That's another story...) Last week I thought the broken breaker bar would make a good handle for the brass hammer I always wanted to make.

I put the bar in the horizontal bandsaw and trimmed up the broken end back to a relatively constant section. Then moved the bar to the lathe and turned the last 1 1/2 inches down to 0.50 inches diameter to accommodate a 1/2-13 UNC thread. I choose this thread because I had both the tap and die: the die to check my work on the lathe and the tap to eventually cut the threads in the hammer head.

I set the spindle speed to 80 RPM (if i recall correctly) and set up the change gears for 13 threads per inch. Set the compound to 29 degrees, the cross slide to zero, and used the thread gauge to verify alignment of the tool to the work piece. Turned on the lathe and made the first light pass. The scratch marks looked like 13 TPI, so I set the compound in another .005" and took another pass. Hmmmm...seems to not be cutting. Did I forget something? Did tool deflection cut deeper than I thought on the first pass? Set it another .005" and made another cut. This time it cut, but poorly, and not on the original cut. Wow. Did I select the wrong line on the threading dial? I thought the manual said I could engage the half nut on any numbered line for odd numbered threads.

Made another pass at the same depth, making sure I used exactly the same number to engage the half nut. no cutting. Attempted to make a couple more passes in .005" increments with similar results. A pass or two with no apparent cutting, then a pass that cut terribly. Lots of noise and the tool seemed to jump around. It seems to be rubbing. And it's not following the last pass. Multiple threads starts now. Is the tool too high? Lowered the tool a little, and it seems to cut a little better, but not like I expected it to.

Went back to check with Southbend's "How to Run a Lathe". First problem is that I had set the compound to 29 degrees to the axis of the spindle, not 29 degrees perpendicular to the axis of the thread. How did this happen? Those are the only marks on the compound, and I had foolishly assumed that they were set up to accommodate threading. Not so. In fact, there is no way to set the compound to 29 degrees for threading by reading the manufactuer's marks. The best I can do is set it to 60 degrees (30 degrees to the thread).

Tried a few more times. No joy.

I removed power and drove the spindle by hand. The tool is definitely deflecting, even though everything is tight and short mounted. What's wrong? I tried the die on the partially cut threads and found there was no way to turn the die without spinning the work in the chuck.

So now I have a theory. The handle is harder than the nails of Hades. Aside from my faux pas in setting the initial angle, I also believe the tool (being a carbide insert I got with the lathe new) is not sharp enough. Finally, I think that when the tool dug in, it spun the work in the chuck and then the threads were no longer lined up, resulting in a new, randomly located cut (appears as multiple thread starts), and it was now too deep, resulting in more tool forces and more tendency to turn the work in the chuck.

Potential remedies include grinding a threading tool from HSS (to ensure it is sharp), making sure the compound is set 29 degrees perpendicular the thread axis, lower the tool a few thousands from on center (or grind the tool with some rake), and annealing the end of the handle with the torch. (It's going to be a hammer after all.)

Thoughts?
Kelly Jones, PE
A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing.
George Bernard Shaw
(1856-1950)

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rudd
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Re: Threading

Post by rudd » Sun Jun 23, 2019 8:56 pm

I think you you've done a good job of analyzing what went wrong. You *might* be able to anneal the bar to get it soft enough to thread. I don't think switching to HSS is going to be better, I think it will be worse as HSS is softer than carbide. I understand the though of trying to be a tiny bit below center, but it has never worked for me. Dead on center, if the tool deflects, it is then below center. So you get the perceived benefit anyway.
Someone will be along shortly to tell you how brass hammers aren't the great idea they seem to be as the face work hardens pretty fact.

Personally, I like a wood or composition handle on a hammer so the shock doesn't transfer to my hand.

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NP317
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Re: Threading

Post by NP317 » Sun Jun 23, 2019 9:05 pm

Yes: Anneal the handle.
Yes: Set the compound to 29 degrees from perpendicular to the rotational axis.
Yes: Make sure the threading tool is sharp and aligned properly.
No: Do not add rake to the threading tool.
Give it a try.
~RN

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BadDog
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Re: Threading

Post by BadDog » Sun Jun 23, 2019 10:45 pm

Yes, it's not uncommon to run across lathes that label compound degrees starting 0 parallel to the lathe spindle axis, you are not the first to stumble onto that issue.

As to what number on the thread dial, go by your manual.

You can reindex the part to finish the thread, I've had to do it a few times. You can get very close, but of course you have to have enough left to clean up any inaccuracies of your location.

I'm not familiar with your lathe, but I've cut threads into hardened material/tools using Top Notch threading inserts. For a smaller lathe there are likely better choices, but my point being that if you have a substantial enough lathe, turning hard steel isn't an issue (obviously up to a point) using carbide. In fact, I prefer it as it generally cuts SO much nicer than typical low carbon steel.

But things get real interesting when you get into spring steels with appropriate harden/temper. The result of that is chips sharp as razors that require a lot of HP (and nerve) to make them break, but otherwise you get endless coils of razor ribbon.
Russ
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Harold_V
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Re: Threading

Post by Harold_V » Mon Jun 24, 2019 2:17 am

I'm troubled by the comment that the additional feed doesn't result in a cut. Something, somewhere, isn't secure, or the tip of the threading tool is badly rounded.

While I agree that a carbide threading tool is capable of performing to satisfaction, one of the places it will fall short is in extracting the tool from the thread at the end of the cut. If a relief isn't provided and one relies on their skill to withdraw the tool when the half nuts are released, you risk hitting the shoulder created from the previous pass, which often results in the tip of the tool being chipped. For that reason, I encourage you to use HSS unless the turn you created was so hard that it required carbide. In that case, you may require the carbide threading tool.

Annealing the end may not be in your best interest, as it may yield a handle that bends readily. A brass hammer is not a great choice, either, due to the already mentioned fact that a brass hammer work hardens way too quickly, and will dent steel. All in all, not a good hammer.

You might consider making a head that will accept Nupla Flex hammer head inserts. That will make a wonderful hammer that has the ability to use heads of various types of construction, yielding a non-damaging hammer with heads that are quickly replaced when needed.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

Magicniner
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Re: Threading

Post by Magicniner » Mon Jun 24, 2019 8:00 am

Harold_V wrote:
Mon Jun 24, 2019 2:17 am
e that a carbide threading tool is capable of performing to satisfaction, one of the places it will fall short is in extracting the tool from the thread at the end of the cut.
So cut away from the shoulder :D

earlgo
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Re: Threading

Post by earlgo » Mon Jun 24, 2019 8:27 am

Reverse threading works only if your chuck is tight and your spindle reverses and your tooling can reach.
reverse threading.JPG
In this case, the chuck didn't matter, but the dog tightness sure did.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

John Hasler
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Re: Threading

Post by John Hasler » Mon Jun 24, 2019 10:07 am

Harold writes:
You might consider making a head that will accept Nupla Flex hammer head inserts. That will make a wonderful hammer
that has the ability to use heads of various types of construction, yielding a non-damaging hammer with heads that are
quickly replaced when needed.

My non-damaging hammer has one lead face and one wooden face (and a wood handle). Can't beat it.

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SteveM
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Re: Threading

Post by SteveM » Mon Jun 24, 2019 10:13 am

earlgo wrote:
Mon Jun 24, 2019 8:27 am
Reverse threading works only if your chuck is tight and your spindle reverses and your tooling can reach.
AND of you don't have a threaded chuck!
John Hasler wrote:
Mon Jun 24, 2019 10:07 am
My non-damaging hammer has one lead face and one wooden face (and a wood handle). Can't beat it.
Yes, but you can beat other things with it.

I hadn't thought about replaceable lead faces. It would be simple enough to make a mold for it.

Steve

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BadDog
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Re: Threading

Post by BadDog » Mon Jun 24, 2019 10:35 am

Harold_V wrote:
Mon Jun 24, 2019 2:17 am
I'm troubled by the comment that the additional feed doesn't result in a cut. Something, somewhere, isn't secure, or the tip of the threading tool is badly rounded.
I forgot to comment on that one. My thought when reading was that with the very shallow infeed angle, hardened steel, perhaps less than perfect edge, and likely small infeed (made tiny by the angle), it may just have skated.
Harold_V wrote:
Mon Jun 24, 2019 2:17 am
While I agree that a carbide threading tool is capable of performing to satisfaction, one of the places it will fall short is in extracting the tool from the thread at the end of the cut. If a relief isn't provided and one relies on their skill to withdraw the tool when the half nuts are released, you risk hitting the shoulder created from the previous pass, which often results in the tip of the tool being chipped. For that reason, I encourage you to use HSS unless the turn you created was so hard that it required carbide. In that case, you may require the carbide threading tool.
Fair point. Not required to work to print, a run-out groove is something that can usually be provided. Cutting away has a similar issue when setting the cut, unless you want a start groove. Hitting infeed simultaneously with half nuts "on the number" (or as mesh if not required) is, IMHO, harder than backing out as disengaged. Either is aided by running slow, which can bring its own issues (particularly with carbide).

However, regarding chipping, that's not at all guaranteed with a slight mistake in timing. I'm not at all sure about other options as I haven't tried them. My first indexed threading tool happened to be a #3 Top Notch that I found left on a scrapped lathe (of all things). Got it for (IIRC) $0.15/lb. 8) Anyway, the inserts for it are remarkably tough and forgiving. I've been using it now for a number of years, and the inserts typically survive a long time that inevitably includes a few mistakes. At first I was daunted by the cost of inserts, but with a local surplus shop and ebay, a few dollars spent has gone a LONG way, and I now regard them as quite a bargain. Downside is that, to my knowledge, there are no full form inserts for it, and there are only 2 generic thread inserts that cover the typical range of 60* threads. So if precise and accurate thread form is required (trough and peak radius), then maybe not the best bet. For my use, which includes not infrequent threading of hardened steel shafts, it is a fantastic option, and I've now expanded it to include the smaller sizes including boring bars for ID threading.

Regarding brass hammer, I agree, not a good choice. But another option would be cast lead. Or, I've seen melted and cast PE head made from milk jugs that might be an option. But I really like the dead blow heads with replaceable faces like Nupla and Lixie. Shouldn't be too hard to make a shot filled dead blow head to take the commercial faces.
Russ
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GlennW
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Re: Threading

Post by GlennW » Mon Jun 24, 2019 11:28 am

BadDog wrote:
Mon Jun 24, 2019 10:35 am
However, regarding chipping, that's not at all guaranteed with a slight mistake in timing. I'm not at all sure about other options as I haven't tried them. My first indexed threading tool happened to be a #3 Top Notch that I found left on a scrapped lathe (of all things). Got it for (IIRC) $0.15/lb. 8) Anyway, the inserts for it are remarkably tough and forgiving. I've been using it now for a number of years, and the inserts typically survive a long time that inevitably includes a few mistakes. At first I was daunted by the cost of inserts, but with a local surplus shop and ebay, a few dollars spent has gone a LONG way, and I now regard them as quite a bargain. Downside is that, to my knowledge, there are no full form inserts for it, and there are only 2 generic thread inserts that cover the typical range of 60* threads. So if precise and accurate thread form is required (trough and peak radius), then maybe not the best bet. For my use, which includes not infrequent threading of hardened steel shafts, it is a fantastic option, and I've now expanded it to include the smaller sizes including boring bars for ID threading.
I've been using that system as well for a number of years and it is excellent.

I have a Comparator, so I use a diamond hone (EZ Lap) and adjust to the required tip radius as needed. Since they are so durable, I now have a number of inserts with various tip radii.
Glenn

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John Hasler
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Re: Threading

Post by John Hasler » Mon Jun 24, 2019 12:07 pm

I wrote:
My non-damaging hammer has one lead face and one wooden face (and a wood handle). Can't beat it.

Steve writes:
Yes, but you can beat other things with it.

I hadn't thought about replaceable lead faces. It would be simple enough to make a mold for it.

I inherited a hammer with two wooden faces pressed into a cast-iron body. It was in poor condition (both faces worn down below the iron, cracked handle, chipped casting). I machined it a bit, poured lead into one face (no need for a seperate mold), pressed a piece of poplar into the other, and made it a new handle. In a year or two I will need to redo the lead face: a ten minute job.

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