Author Topic: A first Engine  (Read 8141 times)

Offline swilliams

  • Full Member
  • ****
  • Posts: 896
  • Canberra Australia
Re: A first Engine
« Reply #15 on: October 29, 2012, 10:16:56 AM »
I'm enjoying watching your progress on this one Dalee. Keep up the good work

Steve

Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13254
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: A first Engine
« Reply #16 on: October 29, 2012, 10:23:06 AM »
Looks like you are making some good progress Dalee. One step at a time and you will be there before you know it with a nice runner as a result.

Bill

Offline dalee

  • Full Member
  • ****
  • Posts: 12
Re: A first Engine
« Reply #17 on: October 31, 2012, 01:46:15 AM »
Dalee,

Sorry about coming in late with a bit of advice.

Almost the easiest way to get your flat bottomed hole is to use a trick that is frowned upon, but can get you to where you need to be.

Drill down as far as the hole needs to be with one size smaller drill than what is needed, then, horror of horrors, mount up a milling cutter of the correct diameter into the chuck and just drill down to the overall depth required. If you take it very steady, that will clean up the bore enough for a little engine such as this, and give you the flat bottom hole that you desire.
I do this a lot when I am putting in counter bores for cap head screws.
I mention this because if you are not taking a lot of material out, then there is not much force on the cutter to cause it to slip in the chuck, which is what would happen if you tried to do full scale milling with a mill cutter in a drill chuck.
Another point, if you do use this tip, if you can, always try to use a centre cutting mill cutter.

With regards to holding small drills. When your finances allow, invest a bit of money in a PIN CHUCK, it will be money very well spent, not just for use on the mill, but on all your machinery that you can drill with, and even by hand using at times, just to do a bit of hole cleaning out or fine countersinking.

http://www.axminster.co.uk/axminster-pin-chuck-set-prod33442/?sessionid=qol

You might also find a set of PIN VICES very handy at times, but not for holding things when mounted into another chuck.

http://www.axminster.co.uk/axminster-pin-vice-set-prod33440/?sessionid=qol

John

Hi,

Yeah using an endmill to make a flat bottom was my first thought also. But the hole depth is just a bit shy of 1.375" deep, (which I didn't mention - my fault  :-[ ). None of my 3/8" end mills are near long enough to reach. I did briefly consider relieving the shank of an endmill, but I wasn't sure I would have enough good shank left to grip properly.

The suggestion to get a pin chuck is good. I didn't think of them and it looks like I should have one. It certainly would be cheaper than buying more drill chucks and arbors. I did look at a tiny drill chuck mounted on a hex shaft at the local hardware store. Very similar to your pin chuck. But the quality didn't look very inspiring as the jaws didn't close evenly. So I opted for the quick change drill bit instead.

I cut a couple of small shafts tonight and turned them to length. Which kind of brings on another question about tooling.

I have noticed that model engines tend to use screw thread sizes, that for me, are a bit odd. Like the 1/4"-32 and 3/16"-36 used in this build. Oddly enough, I do keep a 1/4"-40 tap and die on hand, (useful for small precision lead screws and nuts), and I will swap #10-32 for the 3/16"-36. But do I need to start on a collection of sizes and types for model engineering? Do you buy or make your own taps and dies for this?

dalee

Offline steamer

  • Global Moderator
  • Full Member
  • *****
  • Posts: 10101
  • Central Massachusetts, USA
Re: A first Engine
« Reply #18 on: October 31, 2012, 02:23:58 AM »
The finer pitch threads come in real handy for plumbing fittings...ect.

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline dalee

  • Full Member
  • ****
  • Posts: 12
Re: A first Engine
« Reply #19 on: November 05, 2012, 01:51:37 AM »
Hi,

Well, I have a problem Houston. After making the cylinder, piston, crank disc and pin, I find that either the hole depth is too short or the piston is too long. As it bottoms out on the top of the cylinder. And as near as I can measure, the piston is 3/16" too long.

I have remeasured and rechecked my parts against the print and they are to spec that I can see. So somewhere, some how, somebody made an error. Not really the end of the world.

If I make the cylinder hole deeper, which can be done, will I need to move the intake hole for the air closer to the cylinder head? Or should I shorten the piston more? Does the intake position matter?

Attached is a pdf print, (sorry photobucket is not letting me upload). What I have is the right image. The white is the cylinder housing. The green is the piston. The magenta is the crank wheel. The blue is the standard/upright.

As you can see, the green piston extends well beyond the top of the piston at TDC.

I'm leaning to drilling the cylinder hole a bit deeper and then shortening the piston a bit too. Or have I made a mistake and need to remake some pieces?

dalee

Offline dalee

  • Full Member
  • ****
  • Posts: 12
Re: A first Engine
« Reply #20 on: November 05, 2012, 01:54:51 AM »
Hi,

Awww carp. Ain't no color in the pdf.

dalee

Offline steamer

  • Global Moderator
  • Full Member
  • *****
  • Posts: 10101
  • Central Massachusetts, USA
Re: A first Engine
« Reply #21 on: November 05, 2012, 01:57:45 AM »
no worries Dalee....is the shortened piston still longer than it is in diameter?

IF so ....you'll probably be just fine....otherwise...can you shorten the piston rod instead?

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline arnoldb

  • Administrator
  • Full Member
  • *****
  • Posts: 1337
  • Windhoek, Namibia
Re: A first Engine
« Reply #22 on: November 05, 2012, 05:58:15 PM »
Hi Dalee - good work so far  :)

I just had a look at the plans for this engine and they are pretty confusing when it comes to the measurements, and they just don't add up for me either.
From what I can see, you'd have to shorten the piston by about 1/4" - that shouldn't be a problem as it's running in a cross-head all the way.  Just for clarification for Steamer: there's no connecting rod in this engine; the piston drives the crank directly.
Changing the porting is not much of an option, as you have already drilled some of the port holes.  By deepening the bore, you'll just end up with a lot of "dead" section where the air inside the engine will not be able to exhaust or get air pressure into the engine; and the "dead" section will add a lot of back-pressure from compression resulting in a poor runner.  Having said that, the way the porting is laid out in the plans, it will have quite a significant "dead" space around top and bottom dead center anyway.

I'd just recommend shortening the piston a bit at a time until you can get it to turn without topping out in the bore and giving the engine a go; you might not need the entire 0.625" I'm thinking of.  I'm sorry to say that I don't think this engine design will make a good low-speed low-pressure  runner; it will require quite a bit of air pressure to run... - but it should run.

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline dalee

  • Full Member
  • ****
  • Posts: 12
Re: A first Engine
« Reply #23 on: November 06, 2012, 02:24:36 AM »
Hi,

Thanks for looking at the print Arnold. At least I'm not seeing things that aren't there if it isn't working out for you either. I'm stil having problems getting photobucket to take my uploads. Otherwise I'd post my take of the print.

Well I tried the easy fix by shorting the piston. I took off about .160" before it went over center. Now the piston is so short the top of it actually is exposed at the bottom of the stroke by about 1/32". So, I'm not too encouraged by this development.

I think what needs to happen is for me to remake the upright and then relocate the 1/4" flywheel shaft the .160" lower. I should then be able to remake the piston to original size and it should work. I think this is where the print went awry.

I'm actually enjoying this process. I like the problem solving and it's been an excellent learning experience. Which is why I decided to make an engine in the first place. And a big thanks for the encouragement!

dalee