Worst threading job ever

[mram10]

So I tried threading my bxa post since it didn’t fit correctly. It was 5/8 fine. I cut it down to 1/2 and threaded it to 1/2x16. The nut of course didn’t fit because my thread gauge hasn’t come in the mail and I used the wrong pitch. I cut it down to 3/8x16 and it fit very loose. I will be making a new post when my tooling gets here. Broke 6 tips. Thank goodness there are 3 on each insert. The tooling wasn’t centered on the work with the stock post since I was using 3/8 tooling. I put a file under the tool and tightened it down. Still to low, so I put some washers under the bottom of the tool post.

Setup I used:
Threading with carbide 3/8” Chinese eBay cheapos at 90rpm
Cut to diameter with hss blank, didn’t have time to grind a tip. Ran at 900rpm

Very eye opening. I have a new respect for all those on here that can make a simple threaded bolt

Update: I was using the cross slide instead of the compound slide! Guessing that helped with bit breaking

 

[carlsbad]

You will break a lot more carbide inserts trying to do it "the right way". One reason hss is so popular for threading is that it is harder to break. It takes a lot of practice to disengage the half nut and back the cross slide out at the same time at the exactly correct instant. If you end up going just a bit too far, the insert hits the unthreaded part and breaks. Until you master, you might want to cut a relief groove to thread minor diameter so you can disengage the halfnut into the groove.

Practice on aluminum, delrin, or other soft material.

--Jerry

 

[carlsbad]

PS the threads on your toolpost are almost certainly metric. When you do them, you can't use the halfnut. You have to stop the lathe and run it backwards to get ready for the next pass.

 

[mram10]

Thanks jerry. Great advice. Didn’t back out after disconnect quick enough

 

[watercam]

Other than that it was perfect...
Keep it up!

 

[mram10]

Other than that it was perfect...
Keep it up!

Ha! This machinist stuff is easy

 

[hoz53]

So I tried threading my bxa post since it didn’t fit correctly. It was 5/8 fine. I cut it down to 1/2 and threaded it to 1/2x16. The nut of course didn’t fit because my thread gauge hasn’t come in the mail and I used the wrong pitch. I cut it down to 3/8x16 and it fit very loose. I will be making a new post when my tooling gets here. Broke 6 tips. Thank goodness there are 3 on each insert. The tooling wasn’t centered on the work with the stock post since I was using 3/8 tooling. I put a file under the tool and tightened it down. Still to low, so I put some washers under the bottom of the tool post.

Setup I used:
Threading with carbide 3/8” Chinese eBay cheapos at 90rpm
Cut to diameter with hss blank, didn’t have time to grind a tip. Ran at 900rpm

Very eye opening. I have a new respect for all those on here that can make a simple threaded bolt

Im going to replace the turret style toolpost on a PM lathe with an aloris. I am just going to make a new T nut to fit in the compound. For where you are at and what you are doing it would have been better to use a die IMO. i wouldnt do it that way though id get a new bolt for the tool holder and get or make the t nut.

 

[boltman223]

You have your rpm's flipped around, carbide is ran faster than HSS. Here's a helpful chart and calculator.

https://littlemachineshop.com/reference/cuttingspeeds.php

 

[mram10]

Bolt,
The hss was for turning the shank. Calc said 1300, but 900 was as fast as my lathe would go without changing the belt.
The carbide was used for threading. What rpm would work for 1/2” diameter?

 

[jdh47]

I would advise to take the time to grind a HSS bit for threading. I grind these with the point offset to the left so I can get in close to the shoulder. The bit doesn't have to be 3/8". It can be 5/16 or 1/4". Just adjust it so that the point is on center. If you have a vertical belt sander you can rough out the bit on that before going to the grinding wheel to finish, then hone a little on a good fine stone.

You will need a thread gage to check threads and a center gage to grind your tool bits. Carbide is not very forgiving and it will punish you if you stop it in the cut. HSS works fine for smaller lathes. You can go to Arthur R.Warner Co. tool website and order HSS inserts to replace the carbide inserts in your tool holders.

I wouldn't pay too much attention to the guys that do fast threading. It takes a long time to gain the skills and confidence to do that. Advancing the tool in with the cross slide is fine but only .005 per pass and half that at the half way point. Throw in a few spring passes without advancing the tool past the last pass setting.

Place a magnetic 1" dial indicator on the lathe bed at the point you wish to pull the bit out of the cut. Adjust it's position so that the dial goes less than one revolution and set to 0. About .030-.050 is about right. Adjust the carriage so that the cross feed wheel is at 90* to the bed way. Practice pulling it out when you reach 0 point. When threading pull out with the left hand and disengage the split nuts with the right hand.

An alternate method is to just disengage the split nut at 0 and let the tool cut it's own thread groove at the end of the cut.

Thread at the slowest speed and practice pulling out when it reaches 0. Don't bother admiring your work just watch the indicator. Your threads will be fine. I don't leave the split nut engaged and reverse under power. It is harder on the split nut. It wears it twice as much. You can engage the nut at the same number each time on the thread dial or according to the recommended practice for your machine.

Using the cross feed to advance the thread tool is fine if you remember how much you need to go in each pass. Threading with the compound conventionally is fine also but as lathes get older and things wear more you will get better threads just going straight in. If you do internal threading with a boring bar it is best to advance with the compound because you will be taking off half as much material each pass and tool deflection is a concern.

Whatever method you settle on practice is the key to success. It is pretty cheap to practice on a piece of hot round steel until you get consistently good results. If you can't make a sleeve to build out your T-Nut bolt you may want to make another t-Nut and bolt. It is good practice and you can make it with a flange nut at the top or thread the T-Nut and use a bolt with a washer to fit.

Good Luck

Joe

 

[boltman223]

Bolt,
The hss was for turning the shank. Calc said 1300, but 900 was as fast as my lathe would go without changing the belt.
The carbide was used for threading. What rpm would work for 1/2” diameter?

What material are you using? For turning I would start with the lowest recomended sfm. That's just a starting point. You're going to have to learn how to tell if you need to speed it up or slow it down.

For threading, it depends if I'm threading up to a shoulder or not. I wouldn't use carbide on something that small if I was threading to a shoulder. If no shoulder, with carbide, I would try roughly 600 rpm. With HSS I would start at 400-500 RPM. Rpm is really going to be dictated by how fast and consistently you can pull the tool out. pulling out at the same spot is somewhat important too. And, other times really important.

Being new I would start with HSS run about 150 or less rpm and get comfortable and learn the motions.

Threading at 90 rpm with your carbide is probably part of why you were breaking them

 

[boltman223]

Joe's reply wasn't posted when I first read yours. He's got some good advise.

 

[Hal]

On American made lathes the compound is set at 29*-29 1/2*.
On offshore made lathes the compound setting is sometimes different.

To center your tool bit to the correct height, gently pinch a 6" ruler between the tool tip and the shaft. If it tips away from you on the top its to high.

Hal

 

[GenePoole]

Metric degrees?

 

[boltman223]

Metric degrees?

Its 4 degrees in Tokyo right now.

 

[GenePoole]

Like anything, practice makes perfect. I probably did a hundred threads in aluminum and brass before I cut my first piece of mild steel. I made threading tools out of HSS blanks, parting blades, and brazed carbide tools. I did a dozen practice tenons in mild steel before I got a chunk of 4140PH about 14 inches long. I spent a whole weekend making tenons and parting them off and making another. When I got my first Bartlein blank, I didn't even flinch.

 

[GenePoole]

The mag-indicator idea is a good one, but I like something a bit more rigid. Mighty-Mags are strong, but a little bump and you've lost your zero. I use a tool that clamps to the ways. I like to make a full rotation before zero so I have plenty of time to think about it and get in position to pull out.

 

[boltman223]

A few people have mentioned practicing with aluminum. I look at it a little different, I would start with something closer to what you're going to be using. Might as well start getting a feel for your speeds and feeds right away.

 

[GenePoole]

Another thing I did (and still do) when learning is arrange the controls so that both hands push down when I disengage. In other words, I set the crank candle for the cross-slide to 9 o'clock (or 3 o'clock for internal threading) so that when I reach my pull-out point, I push down to disengage the half-nuts with the right hand, and push down on the crank handle with the left hand to pull out the tool from the workpiece. It is one fluid movement.

Here's a picture showing my setup (for internal threading here). Notice that I also mark my dial with the direction I'll be pulling out:

 

[Shawnba67]

Another thing I did (and still do) when learning is arrange the controls so that both hands push down when I disengage. In other words, I set the crank candle for the cross-slide to 9 o'clock (or 3 o'clock for internal threading) so that when I reach my pull-out point, I push down to disengage the half-nuts with the right hand, and push down on the crank handle with the left hand to pull out the tool from the workpiece. It is one fluid movement.

Here's a picture showing my setup (for internal threading here). Notice that I also mark my dial with the direction I'll be pulling out:

This is very good advise. There is not much time to think at the end of a thread you just react mostly.