george wilson
09-14-2010, 9:07 AM
There is a fairly simple way of making the convex,"threaded",or rope knurls used in the old days for fine work. Objects such as microscopes,telescopes,the cap screws of planes,and a myriad of other high class work employed such knurls. They used to be available in a huge number of patterns. Yet,today,they are hardly ever seen. My friend,the emminent miniature maker,Rivett 608,is the only person I know who has a reasonable collection of old knurls. He is afraid of damaging them,so refuses to use them for the most part. He paid dearly for some of them,too.
These pictures were taken on my Hardinge HLVH metal lathe. It is one of the finest lathes ever made for smaller work,being 11" x 20". It is very good for this type work since it uses collets as well as chucks. Usinc collets ensures concentricity,but also keeps dangerous chuck jaws from flying around close to your fingers. You can also get closer to the work without large chucks in the way. However,a conventional metal lathe is perfectly usable. I used to use a 10" x 24" Jet lathe without collets.
The first pic.on the left is a blank knurl being made from 3/4" 01 drill rod. 01 is less risky than W1,which is much more prone to crack You MUST make the contour very close to the same radius as the tap you are using,or you may quickly find yourself getting a messy job when you try to thread the knurl.
If you are making a concave knurl,and for some reason want to run it against a convex blank,it is even more necessary to make the 2 surfaces THE SAME,or your knurl will not come out.The drill rod will not take much deformation into a knurled surface via pressure rolling before it work hardens,and can damage the knurl you are using as the "mother" knurl.
IMPORTANT: I like to use a 4 flute tap if possible. The flutes are smaller,and the cutters tend to engage at the top of the knurl just as the flute is leaving the cut at the bottom of the knurl. The knurl must be FREE to revolve,or it may stall out while you are cutting it,and make a flat spot,ruining the knurl.
The 2nd. picture shows the knurl holder,which is also made of drill rod,pressing the knurl blank against the revolving tap. Note that the outboard end of the tap is supported in a little female center to keep it from bending and breaking under the cutting pressure. In pic.5,you see the ball bearing dead center I like to use. This center isn't cheap. It is a Royal brand,with roller bearings inside to allow frictionless rotation of the male center. The 2 tubular objects are female centers I made from drill rod. They slip SNUGLY over the male center so the tap can be inserted into them.
The last picture is the knurl holder. It is drill rod. The axle screw is threaded a short distance on 1 end. On the other end is a screw slot. The center area of the axle is left smooth for the knurl to run on. OIL everything when cutting knurls,lest they stall out during being cut.
Another thing: Keep the knurl holder,knurl,and axle free of the tiny,crumbly little chips you will make. MAKE THE WIDTH OF THE KNURL a running,but good fit in the knurl holder,so the tiny chips can't get in and stall the knurl wheel.
The shank of the knurl holder is round. It fits into a 1/2" collet. The reasons it is round are 2: First,you can TILT the holder up to roughly 20º when cutting the knurl,to the RIGHT to increase the angle of the rope knurl. If you cut the knurl with the wheel exactly parallel to the tap,you will get the same angle of thread that is present on the tap. Tilting the knurl holder a bit to the left,you can make the knurl have vertical threads. You can't tilt much to the left,or bad things start to happen. SECOND reason the knurl has a round shank; I can put the knurl in my milling machine,and run the knurl back and forth across an annealed plate of tool steel. This produces a plate like in pic.#4. Repeating waves touching each other. I made this for pressing this design into the back sides of our jewelry either with a rolling mill,or in my 50 ton press I made with a 50 ton bottle jack. All our jewelry has patterned metal on their backs. This makes the jewelry more interesting,and makes the castings look better.
In the BAD pictures of several knurls,on the left end,you can just make out the "wave" knurl. In the picture that shows the wave knurl in front of its "mother" knurl,you see how the knurl was made. First,I made a punch of a single wave. Then,I made a knurl blank with a groove that just fit the height of the wave. Then,I punched the wave all around the mother knurl. It is important that you adjust the diameter of the knurl so that the waves meet perfectly at the last one you punch. After hardening and drawing to a dark brown color,I ran the mother knurl against the narrow final knurl,which also fit into the groove. Thus producing the knurl I wanted.
SOMETIMES I TURN the lathe BY HAND when making a figural pattern like this,to see how it mates up with the mother knurl.
In picture 3 is a BAD picture of the side of a knurl. I always stamp the type of metal on the knurl,and my initals. Hence the 01,and GW which you can make out barely.
As mentioned,I harden the knurls. It is best to STOMP the hole in the knurl tightly with FINE steel wool. Use a flat nose punch. Filling the holes of ANYTHING you are hardening keeps the holes from producing a crack and ruining a lot of work. You NEED TO REMEMBER THIS WRINKLE.
I believe I hardened these knurls in water. You can get by with water for SMALL objects. The water must not be cold. Room temp. is fine. They were hardened at a dark brown color,BUT,the water's minerals turned the knurls bluish. I think it's the iron that does it.
I hope that this information will be useful to those of you who have a metal lathe,and are making cap screws for planes,or for whatever other reason.
These pictures were taken on my Hardinge HLVH metal lathe. It is one of the finest lathes ever made for smaller work,being 11" x 20". It is very good for this type work since it uses collets as well as chucks. Usinc collets ensures concentricity,but also keeps dangerous chuck jaws from flying around close to your fingers. You can also get closer to the work without large chucks in the way. However,a conventional metal lathe is perfectly usable. I used to use a 10" x 24" Jet lathe without collets.
The first pic.on the left is a blank knurl being made from 3/4" 01 drill rod. 01 is less risky than W1,which is much more prone to crack You MUST make the contour very close to the same radius as the tap you are using,or you may quickly find yourself getting a messy job when you try to thread the knurl.
If you are making a concave knurl,and for some reason want to run it against a convex blank,it is even more necessary to make the 2 surfaces THE SAME,or your knurl will not come out.The drill rod will not take much deformation into a knurled surface via pressure rolling before it work hardens,and can damage the knurl you are using as the "mother" knurl.
IMPORTANT: I like to use a 4 flute tap if possible. The flutes are smaller,and the cutters tend to engage at the top of the knurl just as the flute is leaving the cut at the bottom of the knurl. The knurl must be FREE to revolve,or it may stall out while you are cutting it,and make a flat spot,ruining the knurl.
The 2nd. picture shows the knurl holder,which is also made of drill rod,pressing the knurl blank against the revolving tap. Note that the outboard end of the tap is supported in a little female center to keep it from bending and breaking under the cutting pressure. In pic.5,you see the ball bearing dead center I like to use. This center isn't cheap. It is a Royal brand,with roller bearings inside to allow frictionless rotation of the male center. The 2 tubular objects are female centers I made from drill rod. They slip SNUGLY over the male center so the tap can be inserted into them.
The last picture is the knurl holder. It is drill rod. The axle screw is threaded a short distance on 1 end. On the other end is a screw slot. The center area of the axle is left smooth for the knurl to run on. OIL everything when cutting knurls,lest they stall out during being cut.
Another thing: Keep the knurl holder,knurl,and axle free of the tiny,crumbly little chips you will make. MAKE THE WIDTH OF THE KNURL a running,but good fit in the knurl holder,so the tiny chips can't get in and stall the knurl wheel.
The shank of the knurl holder is round. It fits into a 1/2" collet. The reasons it is round are 2: First,you can TILT the holder up to roughly 20º when cutting the knurl,to the RIGHT to increase the angle of the rope knurl. If you cut the knurl with the wheel exactly parallel to the tap,you will get the same angle of thread that is present on the tap. Tilting the knurl holder a bit to the left,you can make the knurl have vertical threads. You can't tilt much to the left,or bad things start to happen. SECOND reason the knurl has a round shank; I can put the knurl in my milling machine,and run the knurl back and forth across an annealed plate of tool steel. This produces a plate like in pic.#4. Repeating waves touching each other. I made this for pressing this design into the back sides of our jewelry either with a rolling mill,or in my 50 ton press I made with a 50 ton bottle jack. All our jewelry has patterned metal on their backs. This makes the jewelry more interesting,and makes the castings look better.
In the BAD pictures of several knurls,on the left end,you can just make out the "wave" knurl. In the picture that shows the wave knurl in front of its "mother" knurl,you see how the knurl was made. First,I made a punch of a single wave. Then,I made a knurl blank with a groove that just fit the height of the wave. Then,I punched the wave all around the mother knurl. It is important that you adjust the diameter of the knurl so that the waves meet perfectly at the last one you punch. After hardening and drawing to a dark brown color,I ran the mother knurl against the narrow final knurl,which also fit into the groove. Thus producing the knurl I wanted.
SOMETIMES I TURN the lathe BY HAND when making a figural pattern like this,to see how it mates up with the mother knurl.
In picture 3 is a BAD picture of the side of a knurl. I always stamp the type of metal on the knurl,and my initals. Hence the 01,and GW which you can make out barely.
As mentioned,I harden the knurls. It is best to STOMP the hole in the knurl tightly with FINE steel wool. Use a flat nose punch. Filling the holes of ANYTHING you are hardening keeps the holes from producing a crack and ruining a lot of work. You NEED TO REMEMBER THIS WRINKLE.
I believe I hardened these knurls in water. You can get by with water for SMALL objects. The water must not be cold. Room temp. is fine. They were hardened at a dark brown color,BUT,the water's minerals turned the knurls bluish. I think it's the iron that does it.
I hope that this information will be useful to those of you who have a metal lathe,and are making cap screws for planes,or for whatever other reason.