Body Knurling Technique?

[Otokoyama]

A number of commercially-produced lights (e.g. Maglite) have bodies that are knurled, only it appears to be the result of a sharp cutting tool, not a knurling tool. The appearance is that of shallow, slow threading (~ .2 tpi). I don't think my mini-lathe would have the torque to pull this off. Does anyone know how this is done? Thanks.

 

[Darell]

One way is to press a sharp wheel into the metal (think pizza cutter, or pipe-cutter).

I should leave this to the guys who actually *do* the process though....

 

[unnerv]

I think you can achieve that look by knurling and then taking a finishing cut across the knurl to flatten the points.

 

[Rothrandir]

i shaved the top on these tips, not sure if that's kind of what you're looking for.

 

[CNC Dan]

Yes, that is how it is done. For the knurling wheels to track in their own groves properly, you need to knurl deeply. If you want a shallow knurl, you turn off the points. You can also just sandpaper the points too. Not the same, but takes off the sharpness.

 

[Darell]

You want DEEP? Talk to Doug Speck. /ubbthreads/images/graemlins/grin.gif

 

[tvodrd]

Just my own observation- my gag3D and MM are simply shallow knurled and not turned afterwards. CNC Dan is right also, but there is an "in between" deep and the situation where you get a fine knurl with coarse knurl rolls. The knurl roll pitch (lines/inch) and diameter in relation to the workpiece diameter also comes into play. Sometimes, you just get lucky and it comes out nice without a hassel. Othertimes /ubbthreads/images/graemlins/rant.gif I suppose I should reread Machinerys Handbook on the subject.

Larry

 

[CNC Dan]

[ QUOTE ]
tvodrd said:
Just my own observation- my gag3D and MM are simply shallow knurled and not turned afterwards. CNC Dan is right also, but there is an "in between" deep and the situation where you get a fine knurl with coarse knurl rolls. The knurl roll pitch (lines/inch) and diameter in relation to the workpiece diameter also comes into play.
Larry

[/ QUOTE ]

That is called doubble tracking. It happens when you don't get a deep enough groove on the first half rev. so that the knurl wheels don't "step into" there own 'footprints'. Sometimes you get lucky, and everything works fitst time. Other times, it's nothing but trouble. What can realy be hard is when a customer wants the knurl to have sharp points, and be a particular diameter.

 

[tvodrd]

Not to mention triple/quadruple and sometimes one wheel will track and the other not! And when you go for a deep knurl, fine flakes of aluminum can be created which can "hammer" into the surfaces of the knurl (even with good cutting fluid) and disloge after anodizing /ubbthreads/images/graemlins/frown.gif . A good wire brushing while still turning in the chuck reduces this. Nice knurls can be a PITA!

Larry

 

[TheFire]

Wow. New things for me to go and try! Thanks guys...

 

[Otokoyama]

Thanks, all.

I thought the body finish was different from knurling, but if it's ordinary knurling then great ... since it's something that I can do. I'm still waiting for LittleMachineShop to get their Large Capacity Knurler back in stock.

When knurling, I turn down the diameter to a circumference that is a multiple of the knurl pitch, and constantly brush while dousing with cutting fluid.

 

[mrsinbad]

[ QUOTE ]
Otokoyama said:
When knurling, I turn down the diameter to a circumference that is a multiple of the knurl pitch...

[/ QUOTE ]

I have not knurled before. Can you explain how you do this? Thanks.

 

[Otokoyama]

You generally need a lathe with a special tool such as I mentioned in a previous post. There are hand knurlers, but I haven't tried these.

 

[McGizmo]

All I can say is that knurling would be much easier if there wasn't a silent K in it!

 

[mrsinbad]

I'm sorry if I wasn't clear in my previous question. i already have a Taig lathe and I hope to buy a mini lathe by the end of this year. What I don't know is the process you follow nor the calculations you need to make in order to knurl.

Say for example I start with 7/8" OD tubing. The circumference would be 2.749". Can you outline what you would do to knurl this tube? Thanks.

 

[Chief_Wiggum]

If you have a knurler already and know the pitch of the knurls, you can calculate the diameter the piece needs to be so that the knurls don't overlap.

Like Otokoyama said, the circumference needs to be an even multiple of the pitch. So if your knurls are say 20 tpi, then then

pitch = 1/20 = 0.050"

2.749 / .050 = 54.98

So the circumference is almost an even multiple of the pitch. I understand that most knurlers have enough slop built in to accomdate a circumference +/-30% of the required.

Did I do my math right? /ubbthreads/images/graemlins/grin.gif

 

[Otokoyama]

Right on, Chief! I think the main issue is getting clean knurling wheel tracking right at the start, and the pitch must evenly divide into the circumference to do so.

While knurling, keep the piece and knurling wheels clean of swarf by brushing, though make sure the brush bristles don't get caught between the piece and the wheels. Also, a "scissors" knurler is probably the best on the mini lathes, since it doesn't need to apply cross slide pressure to be effective.

 

[mrsinbad]

Thanks so very much for the info. Is the secret of a great knurl job many light revolutions while keeping the wheels clean, or deep cuts? Also, how do you advance the knurling down the tube, advance the carriage as you go or unclamp and reclamp? Thanks again.

 

[Otokoyama]

If you unclamp, it's probably difficult to get the wheels to track in the right place again.

I start light, knurl the desired region by moving the carriage slowly back and forth, until I believe the knurl is as deep as it'll get **, then screw the scissors down a little more and move the carriage slowly back and forth again. I'll stop to check results, but never unclamp. ** On my lathe, it doesn't sound like it's straining anymore.

 

[kodiak]

Angle knurling tool slightly 1 or 2 deg. so you are cutting harder and deeper with the front of the tool. One pass only. The more forced coolant the better.