A Straddle Knurler for the Sherline Lathe

[mikey]

When I ordered my knurls, I selected the ones I wanted and Form Rol beveled them for me, free of charge. I ordered straight from the factory and they were very accommodating. Not sure what to do if you buy from a dealer but perhaps a call to Form Rol might be in order? Maybe they have a special code for pre-beveled wheels.

 

[Grinderman]

Thanks for the compliment. Of the two, definitely the Eagle Rock is the better one. It is very solidly built and vibrates much less than the AXA-19. The Eagle Rock K1-44 is the heavy duty version with a set screw to remove and replace the pins. It is much preferred over the lighter duty model that requires the pins to be pressed out. Expensive but it is probably the industry standard tool for this type.

Thanks much for the info

 

[mattthemuppet2]

lovely project! An inspiration to get back to the design of my camjack knurler that I've been thinking about for years.

One pick point though - you can withdraw reamers under power, in fact it's generally accepted best practice to do so. Reversing spindle rotation will dull them, but keeping them spinning as you withdraw them should not. You can stop the spindle then withdraw, but at the risk of potentially leaving cut marks in the bore if there's a little bit of misalignment or spring involved.

 

[mikey]

One pick point though - you can withdraw reamers under power, in fact it's generally accepted best practice to do so. Reversing spindle rotation will dull them, but keeping them spinning as you withdraw them should not. You can stop the spindle then withdraw, but at the risk of potentially leaving cut marks in the bore if there's a little bit of misalignment or spring involved.

Yes, withdrawing reamers (and lathe tools and boring bars) under power are commonly accepted practices. Most people do it this way but that doesn't make it true. When I first started in the hobby, I bought a really nice set of PTD reamers and within a year I had dulled those reamers by going in and out of the hole under power. I had to send those reamers out for sharpening and I asked the sharpening shop how I could make them last longer. The owner of the shop told me to stop pulling them out under power. Lesson learned. Now I own and use Alvord Polk reamers and have used them for 20 years. All still sharp, all pulled out while not under power and none of them leave marks in the hole. Finishes and accuracy are actually better on a single pass, too.

I passed on that info as a lesson I learned. Before doing something like that, I confirm it over time for myself before I recommend it. Doesn't make it true either, but I am comfortable that I did my best to pass on my best experience to others. I don't expect folks to listen to me but at least I tried.

 

[mattthemuppet2]

hmm, but I don't understand how withdrawing any cutting tool under power can dull it, otherwise drills, boring bars and endmills would end up dull too, right? They all cut holes, they all have cutting edges in contact with the hole wall during retraction, just like reamers. The cutting edge is facing the work in the same way, but should be cutting less or not at all on the withdrawal. The only way I can think of dulling a cutting edge on withdrawal is if the reamer is spinning too fast and rubs or if the very shallow depth of "recut" leads to work hardening. No reason why the latter couldn't happen with the spindle off, akin to stoning a cutting edge.

Not looking to pick a fight, I just can't understand the physics behind it nor have I found any other mention of it on other machining websites. When mentioned, the only caveats were: spin slowly/ feed fast, don't leave too little to cut or the reamer will rub, don't reverse the spindle or you'll dull the reamer, don't stop the spindle or you can leave lines in the bore.

 

[WobblyHand]

When I ordered my knurls, I selected the ones I wanted and Form Rol beveled them for me, free of charge. I ordered straight from the factory and they were very accommodating. Not sure what to do if you buy from a dealer but perhaps a call to Form Rol might be in order? Maybe they have a special code for pre-beveled wheels.

I just went through this. Form Rol (actually Form Roll Die Corp.) is pretty old school. I sent them an email to try to order their knurls. After a few back and forths, I got a quote from them. As an FYI, they don't accept credit cards. So I have sent them a check (today). I just asked for beveled wheels in the email. There doesn't seem to be a special part number for the bevels. I also asked them what clearance they recommended between the shaft and the wheel. The Engineering Sales Manager recommended pin to hole 0.0010-0.0015.

I'll be building a straddle knurler based on @mikey's design . No mill in my shop, so I'll have to improvise a bit. Starting a project thread soon.

 

[mikey]

hmm, but I don't understand how withdrawing any cutting tool under power can dull it, otherwise drills, boring bars and endmills would end up dull too, right? They all cut holes, they all have cutting edges in contact with the hole wall during retraction, just like reamers. The cutting edge is facing the work in the same way, but should be cutting less or not at all on the withdrawal. The only way I can think of dulling a cutting edge on withdrawal is if the reamer is spinning too fast and rubs or if the very shallow depth of "recut" leads to work hardening. No reason why the latter couldn't happen with the spindle off, akin to stoning a cutting edge.

Not looking to pick a fight, I just can't understand the physics behind it nor have I found any other mention of it on other machining websites. When mentioned, the only caveats were: spin slowly/ feed fast, don't leave too little to cut or the reamer will rub, don't reverse the spindle or you'll dull the reamer, don't stop the spindle or you can leave lines in the bore.

For reamers, all I can tell you is my experience with them. I've only been using them for 30+ years so I don't know much but I do know that I dulled a number of reamers in my set in the first few years of using them by doing things the way most guys do it. I asked what to do about it and have stopped backing them out under power. My Alvord Polk set has now lasted over 20 years and are nearly pristine so what can I say? It works for me.

As for other cutting tools that are intended for use in one direction, namely boring bars and lathe tools, I can tell you from long experience that pulling them out under power increases flank wear. I have observed this personally so I have learned not to do it. I have chipped off insert tips pulling boring bars out of holes so I've learned not to do it. My HSS lathe tools will dull faster if I drag them backwards out of a cut so I don't do it. I didn't read, watch or hear about any of this; just personal experience, which is why I always tell folks that this is just my way, not THE way, and I mean it.

Do what you think is best, Matt.

 

[mattthemuppet2]

no worries. Like I said, not looking to get into a fight or p!$$ing contest, just trying to understand the rationale and learn something.

 

[DavidR8]

@mikey I'm putting together a material and tooling order for this build.
Is 1/2" O1 drill rod sufficient for the 1/2" O1 tool steel rod?

 

[Grinderman]

This arrangement is really solid; the only movement on the tool are the wheels in their slots at the end of the arms. I left 1/32” of space on each side of the wheels and found that this is all that is necessary to allow them to track and synchronize.

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Could you explain this statement? I thought you were using 1/4” wide wheels in a 1/4” wide slot in the arms.
Thanks