Silver steel crankshaft

[teamrickyParticipant @teamricky]

Better than I can see lol 😂 Zoomed in

[teamrickyParticipant @teamricky]

Nice big grinder 😁

 

I was thinking of ways to make a little tool post grinder or use the over head mill in some way to grind journals …… All good things to think about especially if I’m making a few accurate shafts ! I’ve caught up just now on shafts I need but the next one ?! 😂

[teamrickyParticipant @teamricky]

I’m also glad I made each end a bit longer , I hadn’t had the thought to use a slip eccentric at the beginning but obviously I have extra space for that now ….. And the other end a water pump off take or drive pulley can also fit if needs be !

 

Also just remembered I had made a 3/4” throw built up crank for a little traction engine I’m building, Just took some pictures to show the difference in styles…

And I just got around to finishing and running in my first model engine !

Specs are: Silver steel crank , Stainless rods, Nickel plated con rods, 1/2” bore 1/2” stroke

 

I’m pretty happy it runs at low pressure and you can hear the beats which is difficult sometimes on piston valve engines ! It’s now run in ready for a clean up lol 😂

 

There is a mistake in the build 😁 10 points to grifendor if someone can spot it !

 

 

[Julie AnnParticipant @julieann]

Well done on completing the crankshaft!

I’d make a few observations:

1. Silver steel isn’t the best choice of material. It can be difficult to machine, so why struggle if the part isn’t going to be hardened? The finish on the part as shown isn’t great. Personally I’d have used EN3B, but one could use EN8 as one of its applications is axles and shafts.

2. Picking up on the machining of silver steel if using carbide inserts one needs a high surface speed to get a smooth finish. A perfectly good finish can be obtained by turning; no need to grind. Here is a link to some practical turning tests on silver steel, soft and hardened:

Turning Trials

It looks like the OP of the turning trials is no longer a member; no idea what happened.

3. In my experience a carbide parting off insert is not suitable for general grooving. They chatter badly unless a good feedrate is maintained. When parting off using carbide I use an absolute minimum feedrate of 4 thou/rev.

Julie

[JasonBModerator @jasonb]

Julie, is it me not seeing any images or have all the photos gone from that thread a along with the past member, makes it a bit hard to follownow as the text alone does not show what is being referred to

[teamrickyParticipant @teamricky]

It’s certainly not the easiest material and as you say surface speed is a problem….Especially with carbide and using a drive dog is the only single reason I have lines in the part….. I’d turn that at 2k rpm without the drive dog balance problems

In person without zoom and false light it’s very much ok not perfect but neither am I or my tools lol 😂 I do like a challenge so I’ll probably harden it now a see what happens…

 

Ive got other stock of cast iron but the diameter is probably not big enough diameter to squeeze the part out, For myself using up what I have is where I’m at spend wise on hobby for a little while , Just out of interest I used to do a lot of RC flying and all the cranks are one web mono pin I guess you could say so no support for the other side , The Os 21 used a 5mm pin ! Silver steel then hardened, Intresting the rpm they make and how well they hold up honestly !

 

I might well make more and hone the technique and tooling , Possibly find a hss tool grind that works not sure , My bigger lathe will give the best results due actually having rigidity lol 😂 The Proxxon is great on smaller stock and accuracy and the Emco on larger ,My choice is just for comfort to be honest I can sit at the micro lathe and it’s all very civil 😂

 

Any way it’s been a good challenge at a smaller scale and the part is very much usable and looks fab

[JasonBModerator @jasonb]

Keep the cast iron for something else unless in the unlikely event it is SG iron. Common grey iron will be more likely to fracture particularly if you stick with the indersize pin and load up the ends of the crankshafy with pullies and pumps.

I can’t see your turning tools in any of the photos but what may help if you like Carbide is using the **GT inserts sold as suitablle for aluminium an dnon ferrous as these are a lot sharper so will take a fine cut and also means that the flexible crankshaft is less likely to deflect away from the tool. Even so on the little Proxxy sith a slender crankshafyt like that I would not try the feed rates Julie suggests, might be OK for parting near the chuck but on a job and machine like this I see trouble ahead

This is a slightly larger shaft (10mmdia) I would get similar results using that tool on my Unimat 3 as I am on the W280, these are final finishing cuts putting a slittle load into the shaft as possible to avoid any flexing. That is 1 thou depth of cut and about 1/2 a thou feed. Counterbalance can always be added to compensate for the Dog and the crank itself.

As for crank pins it is not just the diameter to consider. The model aero engine pin is short compared to it’s length manybe 2 x so little leverage. The pin in the middle of your crank will have flywheel, pulley and pump some distance away so that extra leverage will tend to put more load into the small dia unhardened pin in the middle.

[teamrickyParticipant @teamricky]

Thanks for the video of the sharper tool 😁 I’ll see which one would fit my general turning tool .

One thought I had over night is maybe just make my own tool and braze carbide to the end with the geometry I need …. The tool would be to create the slots/crank pins , The off the shelf parting tools have limited reach and I only just squeezed the 3/4” stroke using the tools I had, I also saw on line the other style of grooving/parting tool (flat style holder)

That style looks to have much longer reach when needed ….

That might be ok ? If anyone has experience please let me know 😁

[bernard towersParticipant @bernardtowers37738]

When you say off the shelf parting tools which ones do you mean as insert type blades are more than long enough and trapez type blades in HSS come considerably longer. If you are concerned with rigidity Hss is available in oblong shapes as well.

[JasonBModerator @jasonb]

You should be able to get CCGT and TCGT which are the more common shapes, I like the DCGT shown when using the tailstock for support as you can get in closer before the holder hits the revolving ctr.

Reach should not be a problem with your parting tool as the blade part can be slid forward in the holder. The downside of more stick out is that the interrupted cut tends to bend the blade sideways as there is not a lot of lateral stiffness. You can get over this by roughing out with the parting tool then using either HSS or an insert boring bar to do the finish cuts down the sides of the webs

Then go back in with the parting tool slowly advancing the cut while moving from side to side to finish the pin. If you do find chatter with an insert parting tool then the amount of cutter engagement can be reduced by taking a Dremel type grinding disc and cutting away the central leading edge of the insert so that just the outer edges are cutting. As you are moving sideways you don’t need the but at the front.

You can also eliminate a lot of that initial bang-bang-bang as the eccentric piece of work goes round by milling away a lot of teh waste between the webs. leave say 0.5mm on the sides and similar around the pin. This is a flat crank but you can do it on round ones too.

[JasonB]

On JasonB Said:

Julie, is it me not seeing any images or have all the photos gone from that thread a along with the past member…

The thread was published a long time ago, but I don’t recall there being any photos? I’d guess that unless a finish is really awful it is difficult to distinguish differences from a basic photo. Presumably the OP decided it wasn’t worthwhile adding photos.

Julie

[Michael GilliganParticipant @michaelgilligan61133]

Just for clarity

Verbatim quote from the opening post of that thread:

I haven’t posted pictures of my latest tests as I don’t think my photography is good enough for the pictures to add anything.

MichaelG.

[Julie Ann]

On Julie Ann Said:

On JasonB Said:

Julie, is it me not seeing any images or have all the photos gone from that thread a along with the past member…

The thread was published a long time ago, but I don’t recall there being any photos? I’d guess that unless a finish is really awful it is difficult to distinguish differences from a basic photo. Presumably the OP decided it wasn’t worthwhile adding photos.

Julie

The OP of that thread was former member Andrew Johnstone, who may perhaps be known to you? You posted a pic of a lathe remarkably similar to his, right down to the unusual hydraulic copying attachment and the even more unusual Ainjest threading dial attachment in this thread here https://www.model-engineer.co.uk/forums/topic/making-a-3-saw-blade-clamping-washer-with-a-tapered-thickness/

If you know Andrew he may be able to help you further. My apologies if it’s just a case of identical looking lathes. Just such an unusual combination of accessories it stuck in my mind and made me wonder at the time if you were related to or associated with Andrew, who used to be a prominent poster on here when I was a member some time back.

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