Mount Trapezium

[Michael S.]

The entire setup looks good. There's not much left to do 😉.

Michael

[PaulR]

Your 'trophy' reminds me of the Tin Man somehow! That's a lot of holes and all very neatly laid out, kudos!

[crueby]

Lots and lots of holes! 

[redhouseluv]

The entire setup looks good. There's not much left to do 😉.

Michael

Your comment made me look at the issues of the Model Engineer where the build is documented; I have just realised how much material I need to buy in order to make the bearing stands, bearings, yokes, piston etc, etc ...................better get ordering before I grind to a halt!!!! 

[redhouseluv]

Low supplies has led meant jumping around in the build sequence and making bits with what stock I have.

I made the valve chest cover and my 1st attempt at fishbelly conrods.  I followed an excellent set of instructions from a chap called 'Jason' on the forum 

Thanks, they worked out! 

[redhouseluv]

Advice with crank please

I have not made this type of crank before and was wondering the best & simplest approach - see diagram. At the moment I'm thinking rectangular stock with 2 holes 0.750" apart, stepped roughly to the correct heights for each boss, and then the rotary table to mill the 2 bosses? I think the intersecting piece between the bosses is visually nice and can be filed afterwards?

How do I hold the work for milling on the rotary table; it looks too small to clamp it directly to the table and will a 4-jaw chuck work?

Thanks as always.....

[Jasonb]

Thats the right method

To hold them I would face a bit of 1/2" stock, turn a snug fitting spigot on the end about 2mm long and then drill and tap say M4. You can then centre up your 3-jaw chuck on the rotary table and grip your new arbor with the crank arm screwed to it with a cap screw and washer and mill one end. swap over and mill the other. Not too heavy a cut as the forces want to undo the screw.

Other options are to clamp a bit of scrap bar to the R/T drill and tap one central hole and other your crank throw apart. Then screw crank to that, cut one end and then swap over.

[redhouseluv]

Excellent, a couple of options to think about.....let me see if I have a suitable piece of stock!

[redhouseluv]

It's a good job I'm not paid on piece work as I've made 2 items today (see below). I would have had my wages docked for breaking 1 centre drill, 1 carbide and the first tie rod I attempted! There would have also been a large contribution to the 'swear box'   

Once I made the tie rod and connected it I realised everything was tapering upwards, so I made 2 tiny washers (you may be able to see them on the inside of the guides) which now means there's a taper on 0.005" from the top to the bottom - I can live with that.

Let's see what tomorrow has in store..............

[Jasonb]

The best way to avoid breaking ctr drill is to not use them for anything else except where you intend to use a tailstock ctr in the hole or have another need for the 60deg hole they cut.

Treat yourself to a spot drill which can be used when you want to start a drilled hole. 3-4mm 90deg should cover most model making needs.

Something like this or the carbide option is not a lot more.

https://www.shop-apt.co.uk/nc-spotting-drills-m42-premium-high-speed-steel.html

https://www.shop-apt.co.uk/spot-drills-altin-coated-carbide-90-120-point.html

[crueby]

Center drills have a tendency to not clear chips well, so it works best to 'peck' at the hole if you need to go deep to give a seat for the live center, go in a bit, back out to clear chips, in a bit more... The chips can pack into the narrower tip causing the tip to torque and break off. A bit of oil on it helps too.

[redhouseluv]

Thanks both, I started using spot drills some time ago and agree, they are much better/easier than centres drills if you don't need to use one. That's what was frustrating, I did need to use one as I turned the tie rod between the chuck and a live centre on the tailstock in a pair of homemade bushes threaded to take each end.......not the end of the world! 

Anyway, I think I'll invest in one of those APT spot drills, that'll get use a lot!

[redhouseluv]

Made a jig to hold the work with a small hole in one of the uprights for a pin gauge which I used to centralise it on the rotary table.

It was all going so well and was starting to look like a crank, when I made a dumb mistake and made a piece of scrap - lesson learned and the jig works, so ho hum, onwards and upwards and another go tomorrow......

[crueby]

Yup, we've all been there!  Practice makes prefect. Um, Practize makes perfect... I'll keep practicing too! 

[redhouseluv]

Second attempt at crankshaft

Having learnt from the errors of attempt 1, attempt 2 has has worked out and is correct dimensionally. I just don't know how to get the slant between the 2 stepped surfaces; see pictures 2 & 3 where you can see my piece against the diagram.

I was wondering if it's just a 'nice to have' and while I've the setup still in place I should mill the surfaces to 1 level and lose the step or am I missing something? I really don't want to mess it up at this stage!