Another Potty Horizontal Mill Engine

[Heffalump]

Well after going through three cylinder blanks and each time struggling with imperial to metric conversions I decided I was going to put Elmer's #33 on hold and look for something else, but in metric this time, until I've got a bit more experience under my belt to continue along Elmer's journey. I stumbled upon this one just as Todd was completing his, and happily Stewart was kind enough to send me the latest drawings. I don't expect mine to look anywhere as good as Todd's engine does. I'll be happy with another runner, but I'm going to do my best along the way to make it look as nice as I can, and that started with making my first part twice. (Great start Jim!)

Making the parts in no particular order I started with the Cross Head as it's near the top of the drawing. I didn't take many photos here but you get the gist.

Thanks to Todds thread I was introduced to filing buttons of which I produced two to help me with the curves on the end of this piece. I made them quickly from what I believe is PTFE, to use more as a visual guide than a mechanical aid, but if I ever get round to it I'll make some steel ones and harden them. My M4 threaded section is threaded rather poorly, I believe this is due to poor lathe alignment giving me an oversize pre-tapping hole. I'll use the mill from now on to keep my drilling and tapping aligned. I also managed to bend the part slightly as I took out the middle section, I think I could have done this differently. Anyway. Part one is done and on to the next, probably the crosshead pin. I've not done any finishing on this part - I'm going to buy myself a nice set of different grit popsicle sticks if anyone has any recommendations.





Thanks for looking

[tinglett]

Very cool to see...I'll be following along the whole way!

I found myself deburring with a file immediately (of course) and I'd run the part over sandpaper that's sitting on a flat surface.  That is, sandpaper sitting still and you move the little part.  Like lapping.  I'd rotate the outside curve as I'd draw it across the sandpaper.  Worked pretty fast.

But the insides will need something like a popsicle stick like you say.  Maybe wrap sandpaper on a rod or dowel to get the inside round surface.  I'd do this with ~100 grit (if needed) up to about 200 so the final sanding/polishing work near the end was less of an effort.  Gives you time to mull over the next part too .

Your part sure looks perfect to me.  I like your photos too

Todd

[Heffalump]

next up was the crosshead pin. I've realised now that I don't know how to turn a thread using a die all the way up to the shoulder, single point threading is out of the question as the lead-screw doesn't turn on my lathe. Can anyone help me out here?

Anyway to get started I turned down some slightly over 6mm silver steel to size, "blued" with a permanent marker and marked out.



Next I faced the ends and turned them down to 4mm ready for the M4 thread.



Here's the pin all done...



...and mated with the crosshead.



Nice and easy. I've found machining silver steel to be particularly difficult to get a good finish, I dialled the tool height right in and that improved a bunch, but I think I've still got a way to go.

[tinglett]

Hopefully others can chime in with the threading question.  I can get very close to the shoulder with my dies, and when something needs to thread snug against a face I've used my parting tool to turn down that last small length next to the shoulder so that it won't stop a nut that's threading on.  That's the minor diameter and if the nut is a strong metal it can probably be a smidge oversize so the nut makes threads on it.  I'd use a disposable nut the first time, just in case .  Also, maybe you can try turning around the die to finish it off?  Maybe the back side can get in closer.  I'm not really sure if a die has a direction or not.  I never really thought of that before now.  Certainly it's designed to start on one side.

I hear you on the finish comment.   I was so frustrated in the middle of last year that I started this thread on it:  http://www.modelenginemaker.com/index.php?topic=3946.0 .   I'm getting better at it, but there are still days where I can't get it right the first time, or the second, or....   Certainly a lot of skill is involved with a good cutter and its angle, and it doesn't hurt to have the machine tuned up as best you can get it.  And while the old-timers (that's a compliment!) on this forum will shutter when I say it, you can always hit it with sandpaper to smooth it out a bit .

That part looks real nice, though I think you'll need to get the threads in a little closer.  You'll know when you test fit the slide bars.

Todd

[NickG]

Yes, as Todd said, you need an under cut for the thread if you want the nut to but up against the shoulder. Again, as Todd advised, use a thin parting tool to turn down to just under the minor diameter of the thread so that it clears then threads in the nut. Turning the die around at the end tends to get you a bit closer as there is no or little lead in on the back face.

Getting a great finish on silver steel isn't the easiest. I see you're using carbide tips, speed needs to be higher. I must admit I prefer a nicely sharpened HSS tool although have started using carbide sometimes as you don't have to keep changing tools and re-sharpening!

Good start, keep it up!

[Jim Nic]

A good start, I'll be following along as the cylinder is the same as Stew's Vertical Cross engine which I'll be starting soon.
As far as cutting a thread up to a shoulder, I have found that grinding down one face of my dies allows me to get close but still not all the way in.  A "cheat" I have used when I really need the thread to be tight to the shoulder is not to cut a male thread at all.  I drill and tap the end of the piece to the appropriate thread and then Loctite in a piece of studding.  (I can hear a certain lady screaming "NOOOOOOO" from here    , but it works for me).
Jim

[Roger B]

Most of my dies have a lead on the front face so, as several others have said, turning them round can get you much closer (2 threads?) to the end.

[Heffalump]

Thanks for the encouragement everyone. I'll whip the die around tomorrow and get as close as I can, then I'll remove some material between the threads and the end.

I was planning to need to sand and polish finish each part anyway to get it looking as nice as possible, but now I've worked out that I can't hold the work in the chuck now I've threaded it! I'll drill and thread M4 some spare bar and run the lathe in whichever direction doesn't undo it to finish the part.

Jim - you're not far from me - I'm Bicester. I've thought about the loctited threaded rod thing a few times - but small taps scare me, I've broken too many!

[Mike Bondarczuk]

Hi,

If you can get hold of some ER collets then holding the threaded rods will not be a problem as the collets will hod the work very well but not damage it in any way.

Following your build with interest and may soon be starting a Stewart build myself.

Best regards,

Mike

[Heffalump]

Hi Chaps

I wonder if you can help. I'm really struggling with the slide bars, they are 6.3*6.3*16mm. I'm really struggling to get them down to size AND square. I could buy some 1/4in square bar, but it seems like a lot of expense for the 32mm I need, especially when I have plenty of oversize stock I can use. I think it's because they're so small I'm not sure how to hold them square. In the vice I can only fit one parallel on end due to the small width, but this sits 7mm below the top of the jaws, so is too low.

Any tips on how to hold the work and machine this small part? I'm really frustrated that such a simple item is making me go crazy!

Thanks

Jim

[Jo]

A couple of ideas for narrow parallels  :

Both sides of Tool steel are parallel so you could use that but note that not all tool steel is ground to the same size 

Two small drill shanks of the same size laid side by side can be used.

Let's change the problem: You could use a taller parallel that is wider than the finished size metal and then use a smaller piece of material between the vice jaws and the work to clamp it.

Jo

[NickG]

1/4" square bar is not expensive so long as you can easily obtain it. It need not be exactly 1/4" either - how big is the stock you are using? If it's only a little bigger just make sure it doesn't foul anything.

[Heffalump]

Hi Nick, It's meant to be mild steel but I haven't got any, I'm using inch size ali scrap.

Thanks Jo I might try that last tip, raise the parallels with one laid down in the vice, then some other scrap as a spreader.

I say scrap, scrap seems to be all my raw materials at the moment lol!

I might have to try fleabay.

[Jo]

I say scrap, scrap seems to be all my raw materials at the moment lol!

I might have to try fleabay.

I would take a walk round your local industrial units and see if you can find a machine shop and go on the scrounge

Jo

[NickG]

Jim, I am all for recycling but taking 1" bar down to 1/4" is a lot of extra work, probably a bit wasteful and aluminium isn't ideal for the application. You could probably put that to better use elsewhere one day.

For the sake of £1.32 (I know there will be postage) I would buy a foot of 1/4" sq mild steel, sure the remainder will come in handy on future projects.

It's nice using stuff from the scrap box but sometimes it makes the compromise too much and I've found it much more enjoyable having a set of known materials to suit the job in front of me lately. The quality of your models will improve and also the quality of your scrap box!

http://www.m-machine-metals.co.uk/metals_cs_square.html

Maybe think about this and your next couple of projects and buy a few bits of metal you will be likely to use?