A beginner in trouble with crankshft

[Sam Longley 1Participant @samlongley1]

I am making, as a first project, a Stuart 10 V.

I have just come to the crankshaft which is cast not the current version ( my wife bought me the kit 44 years ago & I have been saving it until I got a decent lathe)

I have turned the main shaft & made an aluminium block & mounted the unit off centre to turn the web. The webs were very thick & to get it down to 17.5mm o/a I used a tungsten tool bit to reduce the outside edges. However, the tool bit will not fit inside the webs so I used an indexible parting tool from the set I bought from Warco. I reduced the webs on the inside to get the gap between them correct & had to take quite a few thou off as the parting tool barely fitted between the casting when i started.

As I got to the shaft ( Which is well oversize & very off centre) there was an almighty bang & fortunately the bit broke rather than the casting. The jig also moved in the 4 jaw chuck

So now I am reduced to using a 1/4 inch HSS steel cutter ground right hand one end & left on the other. It just about fits between the webs as I still have a bit to reduce off them.

The shaft is cast so far off centre that it bashes on the cutter & the topslide visibly moves 3-4 mm ( even my old Drummond had less flex than this Warco)

I am concerned that the cutter will snag & the casting will break

Can any one give me some advice how to do this please, ie what speed & how I can cut the crank shaft between the webs & get it cutting on centre etc- currently it is 2-3mm one side off centre & there is about 3-4mm to come off to get to correct size.It seems that to get the shaft parallel I will need to grind a piece of HSS steel some how or use a parting tool. But the reach needed is quite large to get between the webs

I know I can make a crankshaftfrom steel etc but need to learn how to do it with a casting. Tubal Caine cleverly dodges this in his videos

The flex in the topslide seems excessive & when i used the quick change tool holder on some aluminium the topslide just flexed so much that the cutter just dug in & broke so I have to use the 4 way post which is more rigid. But the reach is a long way for my HSS parting tool which is 2mm * 20 so I need to use my 1/4 inch cutter some how

Any help greatly appreciated— before i go back in the man cave & ruin the thing

[Sam Longley 1Participant @samlongley1]

[Thor 🇳🇴Participant @thor]

Hi Sam,

If yoy have a milling machine you may be able to mill it.

Here's a video, probably a bit larger than yours.

Thor

[JasonBModerator @jasonb]

Your left and right hand tool is the way I do cast and cut from solid crankshafts, come down each side then take the ridge out the middle, you may have to do this a few times.

To cut the bit in the middle I use a 2mm indexable parting tool but keep a tip just for crankshafts that has had the middle ground away with a thin Dremel cut off disc so only the two edges are cutting to reduce chatter. The tool is fed in one or two thouthen moved sideways to take a cut just working back and forth. Similar tools can be ground from HSS so teh end looks a bit liuek a McDonalds "m" but with the legs tapered back for side clearance

Cleans up OK

 

When I did my 10V many years ago I clamped blocks to each end which had he offset ctr holes to use when turning the pin.

Edited By JasonB on 22/03/2016 18:34:46

[nigel jones 5Participant @nigeljones5]

Hi Sam – Jason makes it look soooo easy, but sadly I struggle the same as you do! Mine never look even close to being that good so dont be dissheartened if yours dont either.

[Paul LousickParticipant @paullousick59116]

An external hone can be used to finish the shaft. There was an article in an early edition of ME for making one. Do a Google search for DIY designs.

This one uses a stone from a car cylinder hone.

[John OlsenParticipant @johnolsen79199]

If you have the gear, milling crankshafts between centres is the way to go. You need a mill and some way of putting the shaft, with offset blocks on the ends, between centres. I've done a Double 10 shaft between centres on a Unimat lathe with the milling attachment, just rotating the shaft by hand, so it does not need anything too sophisticated. You still want to take a final skim with lathe tools for a good finish.

Lacking that, you will have to use the narrow parting tool approach. I have done this too, and it can take a bit of patience and perhaps a number of tools, not only left and right but also shorter ones to start and longer ones to finish. The long ones do tend to want to flex sideways. However it sounds like you have flex in the machine itself too…not being familiar with that brand I don't know how to help with that.

You do want to take care that the end load from the centre is not flexing the shaft. It can pay to put something in between the offset blocks and the web to take the thrust, but this must also be held to the shaft so it doesn't fling out and hit you in the face.

John

[duncan webster 1Participant @duncanwebster1]

If all else fails fabricate one from bright bar and loctite. No finish machining needed apart from cutting out the bit of main shaft between the crank webs.

[Paul LousickParticipant @paullousick59116]

John,

I like your suggestion of using a milling machine for rough machining a cast or forged crankshaft to cut thru that tough outer layer.  A rotary table (if you have one) would be a better way of rotating the shaft than by turning it by hand, especially if if is a bigger crankshaft. Then do the finish machining between centres on a lathe.

Paul.

 

Edited By Paul Lousick on 23/03/2016 21:48:19

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