Silver steel crankshaft

[teamrickyParticipant @teamricky]

Hi all,

 

 

I was wondering if anyone is interested in making crankshafts between centres rather than built up or using the 4 jaw ect….. I’ve made a tricky one in the past which turned out good with very little run out.

 

My next project is with my daughter making a Stuart 10v the perfect learning build 😁

 

Pretty much looking at the plans I would go with a one piece crank for simplicity and accuracy so hopefully a start can be made on the part which I’ll cover the steps and results 👍

[JasonBModerator @jasonb]

Seems a waste of a lot of silver steel if cutting it from solid. If you particularly want a carbon steel then why not gauge plate as there will be a lot less material to turn into scrap if you start with rectangular section.

Flat black mild steel bar would be more than adequate for a small Stuart.

[DiogenesParticipant @diogenes]

Please do, it’s always interesting to see other people’s method/approach to making things!

 

[teamrickyParticipant @teamricky]

Hi,

 

Ive got pleanty of stock left over so that did indeed influence my choices ! Agreed you do end up with a lot of swarf but arguably a more scale look , I’ll be milling the webs into counter weights….

[Paul LousickParticipant @paullousick59116]

A friend of mine made a crankshaft for a full size Burrell portable engine from Bisalloy 80 steel plate. Plate was flame cut and then turned on a lathe.

[JasonBModerator @jasonb]

Plenty in stock is a good wnough reason to use it.

I’ve done them from plate, flat stock & round as well as castings. But if you are going with integral balance weights then round is generally the best option.

The original Stuarts were supplied with a casting, though with no material to ctr drill for the throw at the ends were a bit of a pain to hold.

[Charles LamontParticipant @charleslamont71117]

EN1A would be perfectly adequate for a 10V crankshaft, and much better to machine than black bar.

[duncan webster 1Participant @duncanwebster1]

Here’s a picture of how Gardners did it. Note the throw plate at the tailstock end. Compared to this a one throw crank for a Stuart is a piece of cake

 

https://www.practicalmachinist.com/forum/threads/crankshaft-machining-ww1.112643/

[Charles Lamont]

On Charles Lamont Said:

EN1A would be perfectly adequate for a 10V crankshaft, and much better to machine than black bar.

I like to use black bar as there are less stresses within the bar compared to bright, I like my crankshafts to remain straight not go like a banana. Don’t have much of a problem with getting a decent finish on black bar, one I did about a month ago. from black EN3 10 x 30 flat. It’s been upto 3000rpm.

[teamrickyParticipant @teamricky]

Here’s a start 😁

 

There are many ways to index the ends of the crank blank.. Things that have tripped me up in the past is not starting with enough spare length to use for offset turning! Say 3/4” longer as a minimum is a good start, Also if you have a micro lathe as I do the total length needs to fit between centres of which there is two ways to mount the work, One using the headstock Morse taper directly (gives the longest distance) And second which is quicker just simply turn a 60 degree dead centre in your chuck from scrap steel and drive the lathe dog directly off the chuck…

I will try the second method here as the cranks pretty short 😁

 

here’s a picture of the blank bolted to a V block which will be used to achieve indexing to both ends in the same orientation when filipped in the mill, The blank has been centre drilled generously both ends prior to mounting…..More to follow on the actual set up and further drilling…..

[teamrickyParticipant @teamricky]

Here’s the stock all set up

 

The pictures show the V block set up, bolted together

Indexing the end of the shaft in the mill

Checking the results of the centre drilling using poor man’s gauge pins ! Transfer punches

Final set up between centres (off set first)

 

So nuanced points to make ,  Double check your offset from the centre of the stock using a pointed edge finder or similar, Check the stock is definitely vertical when centre drilling the index points, Check after drilling with gauge pins – it’s possible just to turn up two based off your centre drill pilot size if you haven’t any pins to hand!

Those steps ensure the accuracy or the crank pin big end

 

If you haven’t already double check your lathe is not turning a taper, This is a total different subject and process but totally essential for making crank shafts using any method!

 

Next step is to set up in the machine, First is to mock up the stock into the drive dog

Checking it bolts in nicely, Then chuck up a small 8mm dia or so steel scrap, Set up the compound to cut a total of 60 degrees and form a dead centre to the end.

 

With the tail stock live centre installed its then possible to rotate the work by hand and check nothing crashes when turned as it’s very easy to have a clearance problem early on!

 

Tool selection is important, Rigidity is the key, I found the main cutting tool to use will be a 2mm carbide parting/grooving tool , It’s possible to buy radius versions at 2~3mm which would leave stress relief at the edges of all the cuts to be made just like the full scale…

 

Then onto the marking up , A good technique here is to work off the tail stock end using layout dye and callipers, The first cut will be the hardest on the machine and set up being the crank pin big end, This needs to be cut slowly and a little at a time ! Run the lathe as slow as possible use oil if needs be and hone the tool even if it’s new it will all make a difference to how east the cut goes, Oddly I’ve used mild steel and silver in the past and found the silver steel to machine a little better when you take light cuts but the other way around for heavier cuts in offset conditions….

[JasonBModerator @jasonb]

You don’t really need any additional length on the majority of crankshafts. Not only will this allow the shaft to fit on a smaller machine more importantly, by keeping the length to a minimum you reduce the chance of flex and vibration.

[teamrickyParticipant @teamricky]

Just to give some sense of how the job goes have a look at the YT link….

 

Very slow to begin but as the cut becomes longer/less interrupted things become a lot more pleasant!

 

Chatter is likely but take it slow and as long as chips are forming you are cutting 😁

[Nigel Graham 2Participant @nigelgraham2]

Rather than trying to drill centres in the end of the bar itself and hope to have them fully in line, for my steam-wagon crankshaft (one-piece, 2-throw at 90º) I made two square blocks with the centres in those, held to the shaft with 4 grub-screws each while aligned against the milling-machine table and angle-blocks. I made the block bores and shaft oversize so I could skim the grub-screw scars off afterwards.

I would add a photo but I am not sure if I still have them.

[teamrickyParticipant @teamricky]

There are probably a ton more ways to index ….too many to list !

 

Im sticking to one way so it’s easy to follow along 😁

 

Since I’m using silver steel there is no guess work here , Just put the stock between the centres made and sweep the part with a dti on your carriage , this will show any taper about to be produced and in combination with gauge pins it’s possible to check the relationship between any two centres drilled , for maximum accuracy a gauge block should be slipped between the gauge pins rather than the callipers which are just a ball park check

 

If the centres are not to a good tolerance simply loosen the v block and go again !

 

A good tolerance gives nice parallel crank pins and if you are making multi cylinder cranks the strokes need to match up roughly if steam and exactly for Ic engines

[teamrickyParticipant @teamricky]

Here’s some pics during the job 

[DiogenesParticipant @diogenes]

Did you not have some kind of packing between the cheeks.?

[duncan webster 1Participant @duncanwebster1]

When I made an overhung crankshaft from solid I turned the main axle with stock in 3 jaw and support from tailstock. Then mounted a piece of ally (quite large) in the 4 jaw offset by half the crank throw and drilled/reamed through to take the axle. Turn this through 180 in the chuck and the hole is now eccentric by the crank throw. Secure the part machined crank in this hole with a grub screw and machine the crank pin. Same idea can be used for a 2 end crank, and it’s a lot more rigid thzn between centres when doing the crankpin

[Diogenes]

On Diogenes Said:

Did you not have some kind of packing between the cheeks.?

Always a good idea crankshafts can be a bit but clenching🤣

I will sometimes rough out using the 3 jaw as Duncan suggests

But for final finishing I prefer to do it between ctrs, if your 3-jaw is a bit off then finishing each end in the chuck may not result in the two halve sof teh shaft being perfectly in line.

Note the use of a packing piece between the webs in both images. This prevents the crankshaft being distorted by excessive tailstock pressure and also helps reduce flex and vibration which may be why the surface finish in the photos is not ideal particularly towards your tailstock end.

 

[teamrickyParticipant @teamricky]

Here’s the finished lathe work side of things 😁

 

Its definitely a challenge working with a small diameter big end pin…..

 

Once formed I put a solid brass spacer in between the webs to support things when the tail stock was re used to turn the shaft ends down, This is ok but you’ll never get exactly the correct pressure when the jobs done and you release the spacer, Best thing is to leave a little cut remaining, Un mount the shaft remove the spacer and using very light tail stock pressure check with a dti …

 

Its still possible at this point to take an extremely light cut if needs be , After this cut polish if all is good 😁

 

If you still have runout it’s possible the stress in the material has worked against you and a manual tweak here and there straightens things nicely being carful.

 

I can’t stress enough checking your not turning a taper during the process and regularly checking whist cutting gets ahead of any major problems, My machine will turn 5microns or better on a shaft this length but big but I have to set the tail stock pressure exactly! That’s just a limitation of the Proxxon as a lot of the components are aluminium and the ways are not hardened…

 

Next step will be cutting the relief to make counter weight features , Always a bit nervous when everything works out great but there one more cut to do !

 

here’s a YT of the shaft running

 

[teamrickyParticipant @teamricky]

[teamrickyParticipant @teamricky]

Here’s the finished crankshaft 😁

 

Probably twice the hours to make vs built up, But the look in the end will set the entire build off to a good scale start !

 

Final dti checks are good, The diameters all measure good too, I’ve not stated any dimensions as some are personal preference….

 

Another fairly good modification I’ll make is to use a slip eccentric for forward and reverse 

[Charles LamontParticipant @charleslamont71117]

Why is the crankpin so thin, and why not parallel?

[teamrickyParticipant @teamricky]

Hi ,

 

Personal preference on the diameter 😁

 

optical illusion on the pin …. There is an intentional positive radius towards each web just to relieve stress risers , In person it’s very slight and around 0.5mm rad , I used some high speed steel tooling to finish this feature! I covered the radius at the top by means of inserts you can buy rather than hss grinding being covered 👍

[duncan webster 1Participant @duncanwebster1]

What you need is one of these. Made in UK, even better.

For some reason it wont let me paste a link, just google Butler Newall

 

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