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Starting a difficult knurl

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savarin

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#1
I just thought I would sling this up just in case its of help to anyone else.
The knurls on the stainless knobs for my binocular are very very difficult to get to full depth with no double tracking.
https://www.hobby-machinist.com/threads/the-giant-binocular.55688/page-4
What I have resorted to is starting them at the beginning of the shaft but only one third to one half the width of the wheels actually making contact and cutting.
This seems to let me get the full depth of cut easier with no double tracking then slowly move along the bar for the length of knurl required.
If you peruse the knurls in the link above closely you can see some of the double track still visible.
This method of starting appears to have solved this.
 

mikey

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#2
I've done it that way for many years and it works. I mainly use Circular Pitch knurls so the exact diameter is not critical but adequate pressure is, especially in SS because you have to get about a 90% pattern on the first run or you risk work hardening. I've taken to only using knurls with a beveled edge for axial running but convex cobalt knurls would be even better and carbide pins would be icing on the cake if doing a lot of SS knurls.

Haven't seen @darkzero around lately but he is good with SS and Ti knurls.

Good tip, Savarin!
 

benmychree

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#3
I just thought I would sling this up just in case its of help to anyone else.
The knurls on the stainless knobs for my binocular are very very difficult to get to full depth with no double tracking.
https://www.hobby-machinist.com/threads/the-giant-binocular.55688/page-4
What I have resorted to is starting them at the beginning of the shaft but only one third to one half the width of the wheels actually making contact and cutting.
This seems to let me get the full depth of cut easier with no double tracking then slowly move along the bar for the length of knurl required.
If you peruse the knurls in the link above closely you can see some of the double track still visible.
This method of starting appears to have solved this.
I always do it that way, and have for many years.
 

BaronJ

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#4
Hi Guys,

It helps to have the circumference of what ever you are knurling a multiple of the knurl pattern pitch.
 

Bob Korves

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#5
Hi Guys,

It helps to have the circumference of what ever you are knurling a multiple of the knurl pattern pitch.
The diameter/circumference as you are first making contact with the work radially, or the diameter/circumference where the knurl is fully formed, or somewhere in between? Unfortunately, there are multiple circumferences of a knurling job. I understand the theory, and I usually follow it, but I cannot say that my odds of getting a good knurl are increased by doing anything other than starting at the end of the work, which does not work when the knurl is somewhere in the center of the part only. The only other thing that seems to help me (sometimes) is cranking in quickly to engage the part fully. Still, I approach every knurling job with trepidation, more so at the end of a long, fussy job... :oops:
 

BaronJ

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#6
Hi Bob,

As an example, suppose the knurling wheel has a pitch of 1.5 mm. Any circumference that this pitch will divide into should produce a knurl without any overlaps in the pattern.

If you take a wheel and run it over some paper you will be able to measure its pitch. The rest is just a few sums !
 

mikey

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#7
Hi Bob,

As an example, suppose the knurling wheel has a pitch of 1.5 mm. Any circumference that this pitch will divide into should produce a knurl without any overlaps in the pattern.

If you take a wheel and run it over some paper you will be able to measure its pitch. The rest is just a few sums !
This is possibly true if using Diametral Pitch knurls. With Circular Pitch knurls, it is more about pressure.
 

Firstram

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#8
What is a circular pitch knurl?
 

savarin

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#9
In all honesty I have found no difference with using the diameter to pitch method to just going for it hard.
 

Bob Korves

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#10
This is possibly true if using Diametral Pitch knurls. With Circular Pitch knurls, it is more about pressure.
I must admit that most of my knurls came to me from another owner, and though they are high quality, I have no idea of which type they are. I do have some knurls that are known to be diametral pitch, I bought them. Still, though I am using the formula correctly I still get variable results, it is like rolling the dice, in this case I get about 50/50 good and poor results. That is with using horizontal bump pressure, which I well know is an issue. I did purchase a scissors type knurling tool some time ago, but still have not had an occasion to use it yet. I expect it will help, but I am still gun shy...
 

mikey

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#12
I must admit that most of my knurls came to me from another owner, and though they are high quality, I have no idea of which type they are. I do have some knurls that are known to be diametral pitch, I bought them. Still, though I am using the formula correctly I still get variable results, it is like rolling the dice, in this case I get about 50/50 good and poor results. That is with using horizontal bump pressure, which I well know is an issue. I did purchase a scissors type knurling tool some time ago, but still have not had an occasion to use it yet. I expect it will help, but I am still gun shy...
Sometimes I think knurling is made more difficult than it has to be, or maybe my mind is simpler than I like to think it is. If I'm knurling nominal sized stock under 1 inch, I use DP knurling wheels; they were intended for this purpose. If the stock is not nominal, as most of my work is, then I use CP knurls.

It is very rare that I MUST have X-number of teeth around and along the part so I almost never calculate the diameter; I just want a nice knurl with a 90-95% full depth pattern. Using a scissors knurler, I put the knurl half-way on the chamfered end and use moderate pressure to form a single track while turning by hand. Then I turn it again to see if it tracks. If it doesn't then I increase pressure until it does. In almost every case, I can get good tracking by finding the right amount of pressure. Once it tracks, I have two options: I can run it axially in several passes or I can keep cranking until I get a nearly full depth pattern and then run axially. When I do a knurl in SS, I almost always go to nearly full depth before running it down the work piece to minimize the chance of work hardening it. In softer stuff, I usually make several passes. I have found that my finishes are better if I go to part depth and then clean the knurl before going to final depth; fussy, I know.

I used to do the calculation thing when I first started knurling and found that I spent far more time shaving off the diameter by a few thou repeatedly and the damned thing still mistracked. I contacted Form Roll Die and asked for advice about using their CP knurls and was told to just crank down on the knurler and it worked! Now I don't bother calculating, I only use a scissors knurler and I'm a happy boy! I admit that I do calculate things when I want the knurl to come out close to a specific diameter, as when we need a specific press fit, but I can count the number of times that happened on two hands. Most of the time, it is just a decorative thing so I pull out my CP knurls, crank down and go for it.

By the way, Bob, I suggest you go with the scissors knurler. You will find it far more effective and easier to use. I have a shop made one for my Sherline lathe and an Eagle Rock K1-44 for my Emco lathe and am convinced they are the way to go.
 

Bob Korves

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#13
Sometimes I think knurling is made more difficult than it has to be, or maybe my mind is simpler than I like to think it is. If I'm knurling nominal sized stock under 1 inch, I use DP knurling wheels; they were intended for this purpose. If the stock is not nominal, as most of my work is, then I use CP knurls.

It is very rare that I MUST have X-number of teeth around and along the part so I almost never calculate the diameter; I just want a nice knurl with a 90-95% full depth pattern. Using a scissors knurler, I put the knurl half-way on the chamfered end and use moderate pressure to form a single track while turning by hand. Then I turn it again to see if it tracks. If it doesn't then I increase pressure until it does. In almost every case, I can get good tracking by finding the right amount of pressure. Once it tracks, I have two options: I can run it axially in several passes or I can keep cranking until I get a nearly full depth pattern and then run axially. When I do a knurl in SS, I almost always go to nearly full depth before running it down the work piece to minimize the chance of work hardening it. In softer stuff, I usually make several passes. I have found that my finishes are better if I go to part depth and then clean the knurl before going to final depth; fussy, I know.

I used to do the calculation thing when I first started knurling and found that I spent far more time shaving off the diameter by a few thou repeatedly and the damned thing still mistracked. I contacted Form Roll Die and asked for advice about using their CP knurls and was told to just crank down on the knurler and it worked! Now I don't bother calculating, I only use a scissors knurler and I'm a happy boy! I admit that I do calculate things when I want the knurl to come out close to a specific diameter, as when we need a specific press fit, but I can count the number of times that happened on two hands. Most of the time, it is just a decorative thing so I pull out my CP knurls, crank down and go for it.

By the way, Bob, I suggest you go with the scissors knurler. You will find it far more effective and easier to use. I have a shop made one for my Sherline lathe and an Eagle Rock K1-44 for my Emco lathe and am convinced they are the way to go.
Yes, I need to try out my scissors holder pretty soon. I suspect it will work out just fine... Thanks, Mike, for the advice.
 

BaronJ

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#14
Hi Guys,

So CP and DP are just two ways of describing a knurling wheel, otherwise there is no difference between them !
Just another method of causing confusion for the unwary.

Anyway as others have said, just increase the knurling pressure as needed, which is exactly what I do.
 

mikey

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#15
I respectfully disagree, Baron. There is a difference between them and they both have their applications. Using a DP wheel on parts that are not near nominal in diameter (fractional diameters that fall on a 32nd or 64th inch increments) can cause frustrating tracking issues, leading to lost time and parts. They are intended for use in production, primarily. While increasing pressure on a DP knurl can work sometimes, the diameter of the work piece has a greater influence with these knurls.

CP wheels are less fussy of precise diameters, which is a common situation in a hobby shop. There are often times when the diameter on a part that needs a knurl does not happen to fall on a fractional increment but the part is what it is and cannot be changed; in this instance, a CP knurl is most useful. Here, increasing pressure will commonly solve mistracking issues. I don't even bother calculating diameters before using a CP knurl; I just crank down and go.

I own and have used both kinds. At least in my opinion, there is a difference in use and the CP wheels are much more user-friendly.
 

Bob Korves

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#16
So, is there a chart (or other method) anywhere that might tell me which style my existing knurls are by measuring the diameter and maybe counting the teeth?
 

BaronJ

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#18
Hello Mikey,

I don't want to enter into an argument ! My comments were simply that CP and DP are two methods of describing the same thing.

This quote from Bob's link.
Two methods of specifying the comparative tooth spacing are currently in use - CIRCULAR PITCH and DIAMETRAL PITCH.
The second line of my post was a bit tongue in cheek. If I upset anybody then I apologise.
 

mikey

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#19
So, is there a chart (or other method) anywhere that might tell me which style my existing knurls are by measuring the diameter and maybe counting the teeth?
There may be a chart somewhere but I'm not aware of it. I just look the number up when I can identify the maker; otherwise, it is just a guess. Looking at a knurl, it is difficult to tell if it is DP or CP. Near as I can recall, DP is based on teeth relative to the diameter and CP is teeth per inch relative to the circumference and trying to identify a wheel like that is a pain. That's why I don't buy wheels without knowing who made them. Sorry, not much help, Bob.
 

mikey

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#20
Hello Mikey,

I don't want to enter into an argument ! My comments were simply that CP and DP are two methods of describing the same thing.

This quote from Bob's link.


The second line of my post was a bit tongue in cheek. If I upset anybody then I apologise.
I wasn't arguing, Baron, nor did you upset anyone. I just wanted to make the point that there is indeed a difference between the two systems and other than both being knurls, they are not the same thing in design or in method of use.

If you search the site and read the many discussions about knurling you will see that most of it centers around calculating the correct diameter of the part to prevent or avoid mistracking. That is, the poster did the calculations and turned the part to that size and still got mistracking and is confused about why this is happening. No distinction is usually made between CP and DP knurls. Then to make things worse, some old/experienced guy comes along and says, "Well, I just increase the pressure and have no problems." Again, no mention of which knurl system (or knurling tool) he uses. And the confusion continues.

As much as we'd like it to be, knurling is not exact science. Nominal stock is usually not very precisely sized and formulas don't always work. The best we can do is figure out what our knurls require of us and make it so. My DP knurls (I only have two sets and rarely use them) require me to be within a few thou of a 32nd or 64th of an inch or they misbehave. My CP knurls are far more forgiving; I just crank down on them until they track properly and I don't bother figuring out the size my part is. Both types look the same to the eye but they require more or less effort on my part, depending on which is in my knurler.

To complicate things, the knurling tool in use matters. A DP knurl set in a flimsy tool will mistrack horribly, even when the part is correctly sized. Well, at least they did in my hands. It wasn't until I made and used a solid scissors knurler that they worked flawlessly. The same is true for my CP knurls; they work great in my better scissors knurlers than in a flimsy one. My flimsy tool has long since been binned but the lesson is clear - the tool makes a difference.

So, Baron, no argument. My intent was to clarify because a lot of new guys are on this site and knurling has led to more confusion than almost any other topic. It isn't hard to do but you have to use the right tools in the right way.

I wasn't picking on you or trying to start a fight. Just trying to head off more confusion.
 

magicniner

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#21
What I have resorted to is starting them at the beginning of the shaft but only one third to one half the width of the wheels actually making contact and cutting.
This seems to let me get the full depth of cut easier with no double tracking then slowly move along the bar for the length of knurl required.
Nice one! It's firm and confident application of the full depth of cut that does it for me too!
For Cut Knurling on critical jobs I do calculate diameters, for form knurling I don't bother as a couple of better engineers than me or anyone else I know have demonstrated empirically that diameter makes no difference and that technique is the key. (John Stevenson and Joe Pieczynski)
 
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