# Why Do My Threads Look So Rough?



## Jon In Tucson (Apr 19, 2015)

First, let me say that I am a novice when it comes to machining and thread cutting, unless it has to do with using taps and dies.  I have been using some aluminum scraps from a friends work to practice on.  The pitch and diameter of my practice pieces has been satisfactory, although the finish not so much.  Here is what I'm doing:
Spindle speed: 230 RPM, HSS threading tool, Marvel Mystery Oil. 


I tried the threads out and that is the reason for the smooth first few threads.  Thanks for the advice.  God bless.
Jon In Tucson


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## eeler1 (Apr 19, 2015)

Might be the material, some stuff is kinda gummy.   Or maybe you're just not done cleaning them up.   Some  folks run a triangle file thru the threads after to clean them up, or a flat file to break the burrs off of the v.  I often chase threads with a die after to get them nice looking.  Are you feeding in with the compound?


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## Franko (Apr 19, 2015)

I'm no expert on cutting threads on a lathe, but it looks like the tool holder may have slipped. The threads look good on the first few turns, but the buggered up threads are much too thin on the high part of the last 3/4ths of the cut.

I've had similar results when the bit is too high. It will hit a snag and torque down if the dovetail ways are a little loose, causing it to dig in too deep on the last pass. That can happen right in the middle of a pass.

230 rpm is a little fast for threading. Many people just turn the chuck by hand when single pointing threads.


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## planeflyer21 (Apr 19, 2015)

Hey Jon...I'm in Tucson too if you want me to come by and help you out some.

Send me a PM and we can set something up.


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## pdentrem (Apr 19, 2015)

I have seen this on steel as well. Most Aluminium alloys threads like the stuff out of a cow. Have to have a really sharp tool, not the point, just over all and a LOT lube is important. Get the specific cutting lube if Marvel is not the right one. Even WD40 will work in this case. Have the tool set right on center and do not take too deep a cut per pass. 
Pierre


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## Quai_Oui (Apr 19, 2015)

Jon,

When you cut the thread you should make a series of cuts going deeper, with each pass. I work on the basis for threads under about one inch of the first pass being say 1/3 total depth, then reducing this quickly as I go deeper. say 1/6th and halving each pass. As you set the cross slide in, then also advance (in the direction of tool travel)  the compound slide about 1/2 the amount of the cross slide.  This means the tool is then cutting the front face only. As you come near the correct depth make those advances on the cross slide small, and slightly less than 1/2 on the compound slide advance.  If you get this correct, then the back edge of the tool will "chase" the back side of the tread on the last couple of passes. Near the correct depth check the nut each pass, don't remove to much and make the nut lose on the thread. Run a triangular file (with handled) to put a slight radius on the peaks. You can also use a thread file, but the first will give an excellent outcome with some attention to detail.

Also look at which cutting oil you use. I would recommend something like Rocol RTM Metal cutting fluid.  Apply with a  brush to the work before each pass.  Providing you have you tool angles correct, this should give a good outcome regardless of the metal being machined.

Good luck, let me know if I can be of any other assistance


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## Jon In Tucson (Apr 19, 2015)

Thanks for all the input!  I believe that everyone's critique holds merit. 

Eeler1: the material is aluminium.  What type or alloy I do not know as it is from my friends scrap pile at his shop.

Franko:  It is entirely possible that my tool is too high.  I eyeballed it but we all know that isn't the best way to do it. 

Planeflyer21: Thanks for the offer, see your message box.

Pierre: I am also a novice at grinding tools as well as lathe operation.  It is very possible that I have a 60* angle ground on my tool but not sharp enough to cut cleanly.  

Quai_Oui:  The lube is more important than I thought.  I shall look for a more suitable cutting oil than just what I have on hand.  As to the depths of the cuts, I made a series of cuts the same depth.  In the future, I shall make increasingly shallower cuts.  

This is why this is the best forum on the 'net for those wanting to learn how to operate lathes and shop machines.  Good advice offered in a friendly and non judgmental way.  Thanks guys!  God Bless.
Jon In Tucson


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## pdentrem (Apr 19, 2015)

Do you have a Lathe Threading 60 degree "fish tail" gauge? Next a lathe center height gauge? Look up the MrPete YouTube videos, they are an excellent resource. Do not use hot rolled steel like rebar. It is no good to practice on either. The threads will look just like the one in your photo. Use some mild steel, leaded steel or plastic pipe (like the grey conduit 1" stuff) it is cheap and cuts just fine.
Pierre


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## brino (Apr 19, 2015)

Hi Jon,

Forgive me if it is obvious, but you did not reply to this part of eeler1's advice.....

When you advance the tool into the work, are you doing it straight in with the cross feed, or with the compound feed set at 29 degrees?

With the first method the tool is advanced at a right angle to the work and cuts on both faces...it can chatter, especially on a light-duty machine.
With the second method it cuts only on the left face(towards the headstock) 

That fish-tail gauge can be used not only to check that you sharpened the cutter to 60 degrees, but also that you have set it at the proper angle to the work.

-brino


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## markknx (Apr 19, 2015)

+1 brino's post the threads look like they were forced. could well be a dull bit. Also That fish tail gauge can be used to set the tool bit at center.
Mark


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## Jon In Tucson (Apr 20, 2015)

Brino and Mark,
My compound is set at 29*, and I used a fish tail gauge to get the tool square to the work.  I used the cross feed to zero my tool on the work, then advanced the tool with the compound.   The one thing that has been brought  up more than once is the tool may be dull.   My bit sharpening skills need a little practice.   I'm on the learning curve.  God bless.   
Jon In Tucson


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## Wreck™Wreck (Apr 20, 2015)

Built up edge is a likely culprit, inspect the tool after each pass if any material is stuck on the cutting edges you will never get a good finish.


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## gheumann (Apr 21, 2015)

Best lube EVER for Aluminum is "Tap Magic Aluminum" - I love this stuff - better than kerosene or WD40. 

A very easy way to get your tool height set - find the smallest round stock you have - I use 1/8" but use can use 1/2" if that is the best you can do. The smaller, the more accurate. Chuck up the stock and bring the tool almost up to it - then lightly pinch piece of something flat (I use a long xacto blade) between the tool and the round. If the blade isn't vertical, you're not on center. 

I turn a lot of 6061 and thread some - I get better results than you but NOT super smooth. A handheld wire brush on the threads  turning in the lathe is often enough to leave a much nicer finish. If not that, the triangular file.


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## timbertoes (Apr 21, 2015)

29 degrees in the right direction ?...... threads look like narrow and pointy - like mine until it was pointed out that I need to set the  29 from the left hand 45 mark or something like that.  Others can clear that up better than I..  It's been a year ago...


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## Millbo (Apr 21, 2015)

Jon,
The compound will be set  29 degrees to the right from perpendicular to the work piece.
Kerosene is another good cutting oil for Aluminum.
A light pass or two with a flat file followed by a fine wire brush will often take care of the burrs from "gummy" material.

Some technique questions:
Do you have the right relief angles on your threading tool?
Is the threading tool set to the right height?
How much are you taking off with each cut?
Are you taking "free cuts" (not advancing the compound) to compensate for any spring back of the work?


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## Shadowdog500 (Apr 21, 2015)

That looks like a real gummy aluminum.  How does the stuff turn?

Get aluminum that you know has good machinability and try again using all of the advise above.

When I had my mini lathe I used to buy the hobby metals at Ace hardware to keep on hand.  They have a K&S metal bin in every store I've been in with foot long, 1/2" diameter pieces of aluminum, brass, and stainless.  All three machine well using sharp HSS bits. If you can't thread that metal, something is wrong.

Chris


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## stupoty (Apr 21, 2015)

gheumann said:


> Best lube EVER for Aluminum is "Tap Magic Aluminum" - I love this stuff - better than kerosene or WD40.
> 
> A very easy way to get your tool height set - find the smallest round stock you have - I use 1/8" but use can use 1/2" if that is the best you can do. The smaller, the more accurate. Chuck up the stock and bring the tool almost up to it - then lightly pinch piece of something flat (I use a long xacto blade) between the tool and the round. If the blade isn't vertical, you're not on center.
> 
> I turn a lot of 6061 and thread some - I get better results than you but NOT super smooth. A handheld wire brush on the threads  turning in the lathe is often enough to leave a much nicer finish. If not that, the triangular file.



I use that method for centre hight setting, it works pretty good, i use thin shim sheet off cuts.


Stuart


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## markknx (Apr 21, 2015)

timbertoes said:


> 29 degrees in the right direction ?...... threads look like narrow and pointy - like mine until it was pointed out that I need to set the  29 from the left hand 45 mark or something like that.  Others can clear that up better than I..  It's been a year ago...



Yes the Protractor on my Grizzly zeros at parallel to the work so the protractor  reads 61 deg. when 29 deg. of perpendicular. But it does not look as though the back side of the tread is at to great of an angle.
My bet is it is tool bit related, dull , off center, lacking relief, Or feed to fast/deep. As mentioned before the threads look forced.
Mark


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## planeflyer21 (Apr 21, 2015)

I went to visit Jon today.  He had a set of bigger threads (8-10tpi?) he had previously cut and did a very good job, especially considering he is learning everything by reading, trial-&-error.

For his 1/2-28 attempt on aluminum I recommended he sharpen his bits a little more.  Also try some lighter cutting oils.

We were talking about how to get his speed down when he remembered about being able to engage the backgear on the lathe (I'm not familiar at all with Logan lathes).  That dropped the speed down wwaaaayyyy slow.  Too slow for aluminum, so Jon bumped it up to 100rpm which looked pretty good for practice...and about 2 1/2 times slower than he had been before.

The lever that engages the backgear doesn't stay put, so that is something that needs to be addressed.  I did a search and found that quite a few Logans are missing a detent or have other issues with the lever staying put.

For the amount of time Jon has put in rebuilding his lathe and learning, he is doing very well.  He should have some nice, clean threads in the near future.


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## markknx (Apr 22, 2015)

planeflyer21, Awesome. I applaud you taking time to go help Jon. I wish when I started the same way as him I lived in Tucson. But as he did I found my way here. You are the kind of guy that makes this forum great. A big atta boy from me. Thanks
Mark


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## Jon In Tucson (Apr 22, 2015)

Planeflyer21,
It was great to have you stop by and critique my "shop" using that term loosely.  But more importantly thanks for taking the time to offer a little advice.  One of my lessons learned is threading is an operation that can't be rushed, coupled with all of the advice you generously offered, I can make a few changes in how I do things and see better results.  Now all I got to do is find time to put into practice what you recommended.
God bless.
Jon In Tucson


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## planeflyer21 (Apr 22, 2015)

Jon In Tucson said:


> Planeflyer21,
> It was great to have you stop by and critique my "shop" using that term loosely.  But more importantly thanks for taking the time to offer a little advice.  One of my lessons learned is threading is an operation that can't be rushed, coupled with all of the advice you generously offered, I can make a few changes in how I do things and see better results.  Now all I got to do is find time to put into practice what you recommended.
> God bless.
> Jon In Tucson



Thanks, Jon!  I enjoyed my excursion to your shop.

I'm already plotting ideas, er, suggestions on how to get your backgear lever to stay in place.


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## epanzella (Apr 23, 2015)

A quick temporary fix for the missing back gear detent is to get a piece of PVC pipe and slot it so it snap fits over the extended back gear rod to keep it extended.

PS.  Looking at the first post it seems to me the part was bigger than the major diameter when the threading started so that the 60 deg tool turned the OD to a sharp point which the aluminum was too week to support.


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## planeflyer21 (Apr 23, 2015)

epanzella said:


> A quick temporary fix for the missing back gear detent is to get a piece of PVC pipe and slot it so it snap fits over the extended back gear rod to keep it extended.
> 
> PS.  Looking at the first post it seems to me the part was bigger than the major diameter when the threading started so that the 60 deg tool turned the OD to a sharp point which the aluminum was too week to support.



We talked about that.  Jon stated he probably should have turned it down a bit first, as the piece was a stock 0.502" or 0.503".

PVC...pretty simple fix!  I was thinking of making a Z-bar for the knob and affixing a neodymium magnet to the housing. Push it in, held in place.


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## Jon In Tucson (Apr 23, 2015)

As I have been inspecting the back gear drive on my Logan 1957,  I noticed it really growls when ingaged.  Like the root gear clearance is too deep.  Is that a possibility or are they just loud?  It is amazing to me that you expierenced guys can eyeball a picture and really give some very accurate advice and what I was doing on the original piece.  Thanks again for helping out.  God bless.
Jon In Tucson

Sent from my BNTV400 using Tapatalk


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## kingmt01 (Apr 30, 2015)

I haven't got into threading yet but in reading I found a mix of 90% kerosene 10% light oil(they didn't say what light was). I had some 20 at hand so that is what I mixed. It really looked good milling. It was a great improvement over just kerosene which I thought was doing really good to start with. You can also take the smell out of the kerosene by putting some lime in the bottom of it and letting it set a few days. It has a little bit of a sweet smell.


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