GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: Duane38 on February 18, 2021, 03:52:19 PM
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Here is the run down...
Valve half to have 3/4" x 16 internal thread.
Compound set at 29.5 (yes, compound facing correctly), feeding inward to thread, cross slide zeroed and backed away on each exit/backing out pass, thread dial (1-8, set at 1) . Half nut never disengaged as to maintain position.
Bored the hole to the necessary diameter. As I thread, the threads cut, but the bore grows and grows while the thread depth seems to fall short of ever reaching depth. The hole just grows with seemingly shallow threads. I check and check with a thread gauge and the threads never reach depth.
Any advice?
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Have essentially zero experience single-point threading; but are you sure that your insert/bit is ground to the right angle and set correctly? Almost sounds like you have a wider angle than 60* going, so the thread height would never get any taller past a certain point-but the bore ID would.
Hope this helps; like I said zero experience here-only reading and thinking!
Jesse
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Are you advancing the compound feed and also the crossfeed BOTH? (ie both moving the point to a larger radius?.... That could cause what you are seeing....
You have to EITHER use the compound feed OR the crossfeed, but not both.... Using the crossfeed causes the point to cut on both sides, using the compound feed cuts only on one side of the tool bit.... As you said, a 29.5 deg. compound angle is usual for a 60 deg. point on the tool bit.... but then you should only be feeding with the compound....
Bob
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is the cutter fully relieved on the sides and front ?? the bottom of the 60 degree tool could e rubbing the wall of the tube and thats even more prevelent on smaller i.d tubes.
threading internal i usually relieve the cutter a bit more than 60 degrees on the Z - side( chuck side ) .. So yes i end up with a 58 degree tool , but it always makes a perfect 60 degree thread ( or close enough ;D
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Yes, Rob, that is the most likely scenario.... the tool bit is touching below the cutting edge, where it should be ground for clearance....
Bob
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Yeah, advancing only the compound in the thread.
Using a thread bar which has flats for tool holder set screws. The flats are arranged so the tool tip a few degrees down.
Used this one before on 3/4 or 1 inch holes I'm pretty sure. Maybe 1 inch holes.
This could be the problem: tool too big for the hole, maybe.
I'll fool around with it and further troubleshoot.
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Yes, Rob, that is the most likely scenario.... the tool bit is touching below the cutting edge, where it should be ground for clearance....
Bob
Thought of that, but the threads are super clean. Wouldn't the threads show signs of roughness?
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is the cutter fully relieved on the sides and front ?? the bottom of the 60 degree tool could e rubbing the wall of the tube and thats even more prevelent on smaller i.d tubes.
threading internal i usually relieve the cutter a bit more than 60 degrees on the Z - side( chuck side ) .. So yes i end up with a 58 degree tool , but it always makes a perfect 60 degree thread ( or close enough ;D
You know, could be. This is an indexable insert. Suspect the sides are not relieved more.
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The only other thing I can think of is you are using an 11ir a60 insert tool. It has a pitch range from 16-48. If this is the case, the tool height adjustment can be off and the insert can start shaving the bore before reaching full thread depth. I have had trouble getting external threads to 16 pitch depth before tool starts to shave (with some cheap inserts).
You can check your insert against a 16 pitch bolt thread to see how close the flat is to the thread peak.
Dave
Was typing while you posted that
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Here is the run down...
Valve half to have 3/4" x 16 internal thread.
Compound set at 29.5 (yes, compound facing correctly), feeding inward to thread, cross slide zeroed and backed away on each exit/backing out pass, thread dial (1-8, set at 1) . Half nut never disengaged as to maintain position.
Bored the hole to the necessary diameter. As I thread, the threads cut, but the bore grows and grows while the thread depth seems to fall short of ever reaching depth. The hole just grows with seemingly shallow threads. I check and check with a thread gauge and the threads never reach depth.
Any advice?
Cutting tool is rubbing away diameter before full thread form is achieved because its not set to correct height...and the body of the bar is rubbing in the bore...even the tiniest unseen contact can do it..
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is the cutter fully relieved on the sides and front ?? the bottom of the 60 degree tool could e rubbing the wall of the tube and thats even more prevelent on smaller i.d tubes.
threading internal i usually relieve the cutter a bit more than 60 degrees on the Z - side( chuck side ) .. So yes i end up with a 58 degree tool , but it always makes a perfect 60 degree thread ( or close enough ;D
You know, could be. This is an indexable insert. Suspect the sides are not relieved more.
YEA , a lot of my china carbide insert tool holders have no relief on any side.. which goes unnoticed on external threads, not soo much on internal.
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Okay... Checked everything a third time over. I suspect it is the insert. The side profile really does appear to be "dang" near 90 degrees from the top.
So, ordered another threading tool from LMS ground properly from HSS. Will give it another go once the tool comes in.
With that, may go for a bigger hole/bore so the valve doesn't have to be as long.
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Thinking on threads... Did some calculations... Would it be safe to go with a 7/8-20 thread with an outside diameter .995?
Valve body is 7075-T6 (female thread) and the valve exhaust end (male thread) will be 303 stainless.
Valve pressure 2-2.5kpsi. I know that leaves a rather thin wall section.... May stick with 3/4 just to safe. Don't want the valve popping apart.
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.995-.875 thread root =.060 wall in 7075, youd be fiine .
thats assuming the threaded section is seeing pressure , if the oring is inboard before the threads, the 1502lbs could be greatly reduced.
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.995-.875 thread root =.060 wall in 7075, youd be fiine .
thats assuming the threaded section is seeing pressure , if the oring is inboard before the threads, the 1502lbs could be greatly reduced.
Yes sir. Oring will be inside ahead of the threads..
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Phil, what machines do you have......or have access to?
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Phil, what machines do you have......or have access to?
Sieg X2D mini mill
Grizzly G0759 7×27 mill
Grizzly G0765 7x14 lathe
Grizzly G9972Z 11x26 lathe
Own these machines.
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Hi Phil, If the tool isn't cutting to depth it sounds like the radius on the front of the tool is to big, or the angle is somehow greater than 60 degrees. hth.
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Hi Phil, If the tool isn't cutting to depth it sounds like the radius on the front of the tool is to big, or the angle is somehow greater than 60 degrees. hth.
Pretty sure it's BOTH! Rats! All good. Have a proper tool on the way snail mail. Tried to find where I got it from to track down thread specs it can cut. Thinking it is for larger threads with a large root.
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Hi Phil,
You're using insert tooling...assume the geometry on the insert to be correct. The "flat" on your cutter shank should be horizontal, insert will be tipped downward.
A shot in the dark here, but some lathes (like the Smithy I learned on) are not at the "30degrees" you NEED when set AT 30degrees. With some lathes, you need to set @ 60 degrees. Having this wrong, produces a mess similar to what you describe, and THIS was the "hump" that I struggled with learning to single point.
If you look at it from the top, does the compound actually appear to be on the correct angle to follow the desired thread profile?
Aside...good to see you still kicking around. :)
Regards,
Al
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Hi Phil,
You're using insert tooling...assume the geometry on the insert to be correct. The "flat" on your cutter shank should be horizontal, insert will be tipped downward.
A shot in the dark here, but some lathes (like the Smithy I learned on) are not at the "30degrees" you NEED when set AT 30degrees. With some lathes, you need to set @ 60 degrees. Having this wrong, produces a mess similar to what you describe, and THIS was the "hump" that I struggled with learning to single point.
If you look at it from the top, does the compound actually appear to be on the correct angle to follow the desired thread profile?
Aside...good to see you still kicking around. :)
Regards,
Al
Hey, buddy. Yeah, I'm still around! Been super busy over the past few years... I'm more settled in and in the Northern Virginia/D.C. region. Heck, been here almost 9 years now. Sure doesn't feel like it with how fast paced life is out here. Hope you've been well.
Sure enough, the tool does tilt toward by design. Also did check the compound angle in relation the the cross slide with a degrees too once squaring up the tool post with the chuck. Everything is up to snuff.
The carbide insert which came with bar/holder does seem to have no relief. The threads are pretty and crisp, but the bore just grows and the threads seem to meet a certain point in depth until it grows again. In fact, the threads get to a little more than 50 percent of what the thread gauge is before growing bore larger. Also, have a threaded tester that felt real tight upon threading in, then suddenly super loose.
I'm canning that tool for this project. Ordered a properly ground HSS solid inside thread tool from LMS.
This weekend the valve will be completed.
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I have not tried this, but it looks interesting.
https://www.youtube.com/watch?v=f-YWsgAHR6A (https://www.youtube.com/watch?v=f-YWsgAHR6A)
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Really clever, and something I have never thought or heard of.... 8)
Bob
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Saw that the other day when it came across my tube notification. I like Tony. Amusing and educational!
I'm gonna try this out several times as a test....
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Yay! I did it. Finally!
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Yay! I did it. Finally!
nice , looking forward to the tube and lever assembly.