Anti Pull Out Fixings - Another Visit

[Anorak Bob]

Last year, I commenced work on a 19mm thick aluminium table lowering plate for my bitty mill. Got as far as making a few non standard M12 nuts and then the project stalled (sadly a recurring theme). Spurred on recently due to some fiddling around with my Haimer Taster, I thought I would try my luck with a splined fixing along the lines of the splined studs used in wheel hubs as suggested by British Columbian Pete - https://www.woodworkforums.com/f65/an...1/#post1568714

Rather than launch into it it I thought I'd make up a test piece from some scrap. So this morning I formed a knurl on a piece of 20mm 4140 and pressed it into a slightly oversize hole I'd bored in the end of a 500mm length of 32 x 6 aluminium flat bar. With the 20mm stud gripped firmly in the naked jaws of my vice, I was unable to twist the aluminium bar off the knurling. The stud rotated in the vice jaws. The vice was that tight I had trouble loosening it. I maanaged to twist the bar off when there was about 2mm of spline engagement

I can't use over the counter studs. I found some long but not long enough Holden M12 studs on Ebay. They were about 80mm long. The table's centre stud is about 120mm in length.

My plan is to make the three studs required, each with a knurled 20 x 6 head and a 12mm plain shank, threaded only to accommodate the length of the oversize nut and it's oversize washer. I'm hoping that pressing the head not all the way into a 7mm deep hole might lessen the chance of deformation of the 20mm aluminium, by preventing the bulldozed displaced metal from obstructing things. I could well be dreaming.

BT

[jack620]

Nice knurling tool Bob. I notice that, unlike me, you managed to get the slots for the knurls central in the arms.

[Stustoys]

I'm hoping that pressing the head not all the way into a 7mm deep hole might lessen the chance of deformation of the 20mm aluminium, by preventing the bulldozed displaced metal from obstructing things. I could well be dreaming.

Hi BT,
Not sure I like the sound of that(although you know how hard it was to press it together). Wouldnt you just bottom them out when you tighten the table? or worse in use?

How about a 20mm head 6mm thick, a 16mm knurled shank(depending on clearance on your knurling tool)13ishmm wide, and then your 12 shank. Any bulldozed metal will either fall off or you will be able to remove it, instead of it being at the bottom of a blind hole?

Stuart

[nearnexus]

Why even use a round head and a knurl ?

Why not use a lozenge shaped head and sit it in a short mill recess to stop it turning ?

Much the same as I did below.

recess.jpg

Cheers

Rob

[Stustoys]

Don't listen to the first guy, I like this idea much better

Stuart

[Anorak Bob]

I'm thinking the lozenge looks like the winner too. Thanks Rob and thanks Stu for pointing out my brain was in neutral when I typed out the 7mm deep hole comment. Of course the stud would pull up.

Bob.

[Ueee]

Hi Bob,
Nice work and pics as always.
Whilst i can't add anything to your ideas, i was wondering how the straight knurls go in the scissor, do you have problems getting both wheels to lineup, or do they sort of self align once you start cutting?

Cheers,
Ew

[Anorak Bob]

Hi Bob,
Nice work and pics as always.
Whilst i can't add anything to your ideas, i was wondering how the straight knurls go in the scissor, do you have problems getting both wheels to lineup, or do they sort of self align once you start cutting?

Cheers,
Ew

To be honest Ew, I reckon today's the third time I have used straight wheels. The first time was on a lock "nut" I made for my little pretend slotting head. I didn't make a mess of it so I reckon they must self align. If I had made a mess I would have turned the mess off for another crack at it. The second time was to knurl some anti rotation splines on a brass saw nut a couple of weeks ago. My technique was a touch brutal for the delicate brass. Did the job but I'm thankful the knurling is hidden from view. Those wheels were too coarse.

If you need a pair of 3/4 x 1/4 x 1/4 straight wheels, as pictured, let me know.

BT

[RayG]

Hi BT,

I can't offer any brilliant suggestions to solve your problem, well, except perhaps to suggest you look at how they do self-clinching fasteners.. PSM International

***BUT*** I'd love to hear a step by step account of how you get such crisp knurling...


Regards
Ray

[Anorak Bob]

Hi BT,

I can't offer any brilliant suggestions to solve your problem, well, except perhaps to suggest you look at how they do self-clinching fasteners.. PSM International

***BUT*** I'd love to hear a step by step account of how you get such crisp knurling...


Regards
Ray

I reckon it's all in the wheels Ray.

I slipped a bit of 4140 in the chuck and turned some steps on it to see how the 19 tpi wheels would cope with the various diameters. The knurls form rather than cut. All I did was wind down the handle until the kurling was fully formed. To check progress I stop the lathe with the wheels engaged. I knurl at the lowest speed, on my Hercus , 100rpm. Normal running 9 inch Hercus's run 60 rpm.
I used way oil as lubricant, a ridiculous stunt because the resultant slurry didn't help the finish. Dave J uses coolant with good effect. If I could get hold of some cheap used ATF I'd set up an overhead can , a line and a tap and use the transmission fluid to irrigate the knurling.

Rather than the suck and see technique I have gotten away with so far I should be calculating the ideal workpiece diameter based on the wheel pitch and workpiece circumference. In James Harvey's Machine Shop Trade Secrets he suggests turning a diameter a few thou larger than the calculated diameter, lightly engaging the knurling wheels on the workpiece and turning the spindle by hand to see if the pattern repeats. If it doesn't , you turn off a few thou and have another go. And another go and so it goes on. He also suggests WD40 as a lubricant.

My knurling tool was based on a photo I saw years ago on the Hemingway Kits site - Hemingway Kits Knurling The castellated affair on top is my concoction.

BT

Edit: on closer inspection (enlarging the photo) the middle knurl is shabby. Maybe I need to dust off the calculator.

[RayG]

Thanks BT,

That's pretty impressive.... We don't currently have the capability to produce anything nearly as good as that!...




Getting good quality knurling wheels is probably where I need to start.. The scissor style looks like the way to get started...

Thanks for the inspiration!

Regards
Ray

[Anorak Bob]

Thanks BT,

Getting good quality knurling wheels is probably where I need to start.. The scissor style looks like the way to get started...

Thanks for the inspiration!

Regards
Ray

Should you choose to go the home made route and to utilise the, fairly easy to buy cheaply on Ebay USA, 3/4 x 1/4 x 1/4 wheels, I still have a pair of those 19 tpi straight knurls that I'm happy to put your name on Ray.

BT

[Bryan]

Bob are your wheels from Hemingway as well? I bought cheap ones and they have a rough (drilled) bore which is chewing my soft pins up. The Hemingway site says their wheels have a honed bore so I think I will try them. What are you using for pins and how do you lube them?

[Michael G]

I use grease Bryan. My Aloris knurler has pins that look like a button head capscrew with the thread removed from the bottom half (sorry - no pics at the moment. Too many km away from the shed).
For those concerned about daggy looking knurls, after knurling give them a good wire brushing. Some of the daggyness is burr. I find brushing removes that and makes things look a lot better.

Michael

[Anorak Bob]

Bob are your wheels from Hemingway as well? I bought cheap ones and they have a rough (drilled) bore which is chewing my soft pins up. The Hemingway site says their wheels have a honed bore so I think I will try them. What are you using for pins and how do you lube them?

Bryan, The only thing Hemingway provided was the idea.

The Accu-Trak and Reed wheels pictured are from Ebay. The three pairs of spiral wheels I have were purchased from Blackwoods. The were made by Woodside Die Sinking in England but a check a moment ago on the WDS website revealed an absence of wheels. D and D Barry are the Australian agents for WDS. Their website shows knurls but there is no indication that they are English. D&D Barry - Product Range

Brown and Sharpe were also another manufacturer of quality knurling wheels. Let Ebay be your friend.

Bob.


ps. Sorry Bryan. The pins are Unbrako dowel pins and I swipe a bit of grease on them when I dismantle the thing for cleaning and wheel changes.