Author Topic: Old School Barstock 2 Stroke  (Read 79345 times)

Online Roger B

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Re: Old School Barstock 2 Stroke
« Reply #15 on: February 15, 2016, 08:08:39 PM »
I have hopefully invited you to a dropbox that contains the pdf
Best regards

Roger

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #16 on: February 15, 2016, 09:17:23 PM »
Some advice please.--Before I go any farther with this design, I decided it would be smart to see if the main body was going to fit into my 12 x 28" metal lathe and still spin for boring the main bearing hosing. It does---but it's darned close!! In the first picture, you see the body at 1:1 scale mounted and centered in the 4 jaw chuck. The top of the most extended jaw clears the nearest obstruction to the center by a good 1/2". In the second picture, I have rotated the four jaw to the point where you can see how far that same jaw actually sticks out past the chuck. ---Scary stuff indeed!!! That jaw is held by two complete turns of the chuck key so, two turns of thread engagement between "not connected" and "up tight against the part". Balance will be totally out the window--I'm aware of that, but won't be turning at a high speed so it's not that big a deal. The third picture shows the full scale cut-out of the main body laying on the faceplate. It looks like some form of attachment to the faceplate would probably be safer and less apt to fly out and damage the lathe or me. The only thing I can think of right now is that profile of the part is the 'finished" profile. If I started the operation with the part 2" wider, I could put a bolt hole on each side of the part in the "extra" material and bolt it to the faceplate (tap the faceplate if I have to) and finish all the boring, and then after removing the part from the faceplate cut away the extra material and finish the profile. I'm open for reasonable suggestions here.---Brian



Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #17 on: February 15, 2016, 11:52:41 PM »
 The total length of that part shown is 5.009", with 4.019" from the center up to the top of the cylinder. If I start with a piece 8 1/8" long and center it on the faceplate, that will do away with any balance issues. I have to think on the quickest, cheapest, securest way of attaching it to the faceplate yet. The finished  width of that part is only 2.27", so if I buy a piece of 3" stock, that will leave lots of room on each side of the cylinder portion for bolts, and maybe tap the other end of the part on center and bolt thru from the back side of the faceplate thru one of the slots.

Offline Hugh Currin

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Re: Old School Barstock 2 Stroke
« Reply #18 on: February 16, 2016, 12:28:05 AM »
Must be a reason, but why not use a boring head on the mill? Spin the boring head rather than the whole part.

Inquiring minds and all.

Thanks.

Hugh
Hugh

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #19 on: February 16, 2016, 01:11:48 AM »
There is a dirty little secret to boring something in the mill. If its a "completely thru" bore, there is no problem. if it is a blind hole, then there is no problem, assuming you can mount it with the open side up. The problem comes when you have something like a hole thru the center of this block where the crankshaft ultimately goes--The hole is larger in diameter in the center of the block than it is on the outsides of the block. In a lathe, that is no problem, because you can wind out the cross slide while the piece is turning, and the boring tool will cut it's way out to the larger diameter . In a mill, unless you have a very specialized boring head, (which I don't) you have to shut the mill off to advance the boring tool. Do you see where I am going with this? You have to advance the tool into a stationary part. Then you have to restart the mill with the tool already jammed into the material.--Not good!!! And every time you want to advance the boring head, you have to stop the mill to do so. It gets really nasty, really quick!!!

Offline Dave Otto

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Re: Old School Barstock 2 Stroke
« Reply #20 on: February 16, 2016, 01:17:34 AM »
Or you could use a key seat cutter with your rotary table.

Dave

Offline Stuart

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Re: Old School Barstock 2 Stroke
« Reply #21 on: February 16, 2016, 07:23:37 AM »
Brian

Faceplate job for sure , using that it's safer , it lets you put balance weights on.

The out of balance on a relatively small lathe ( not a large industrial machine ) can cause the bore to be out of round due to torque stress in the machine.

Not saying you cannot chuck it ,it your call


Stuart
My aim is for a accurate part with a good finish

Offline Jasonb

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Re: Old School Barstock 2 Stroke
« Reply #22 on: February 16, 2016, 07:32:17 AM »
Bar and two bolts to hold the top, clamp and packer to hold the bottom. Add weights where teh blue marks are to balance.


Offline Ramon Wilson

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Re: Old School Barstock 2 Stroke
« Reply #23 on: February 16, 2016, 07:45:09 AM »
Brian - you could take a look here http://www.modelenginemaker.com/index.php/topic,3233.15.html reply 18. I have always tried to ensure the bore and one face are square to each other on that first set up even with clamps. Leaving material on as a means of future holding is always a good thing too.

Good luck with your project

Ramon
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #24 on: February 16, 2016, 02:53:16 PM »
Jason and Ramon--thank you both very much. Ramon, that link you gave me is priceless--It basically outlines every step i will need to mill my main engine body.---Brian

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #25 on: February 16, 2016, 08:04:38 PM »
My plan at present is to do the cylinder bore on the lathe. It will be a "second operation" after the crankcase bore for the crankshaft is finished. that way I won't be boring into a blind hole, the drill and boring tool will break thru into the cavity already machined in the first operation. As you can see in some of the model cross sections, the cylinder bore is not a smooth stepless bore all the way through. There is an enlarged area part way down the bore for the water jacket, which again would be difficult to accomplish on the milling machine.

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #26 on: February 17, 2016, 06:14:55 PM »
Since I already have a pretty good knowledge of all the operations required except for the piston and liner, I will start with them. This quest is taking me in new and different directions than I have ever gone before. The consensus seems to be that what I want to do regarding the piston/cylinder fit with no rings is indeed possible, but I am going to have to learn lapping skills that I currently do not have. So---I have today ordered a 15/16" internal barrel lap (which will easily expand to 0.945" or 24 mm) and a tube of 8 micron to 12 micron "light" diamond lapping compound. I looked at external manual hones, but as they cost upwards of $400 I will probably be making my own external lap, (pending some information from Ramon on HMEM) from a piece of brass with a hole bored thru it and a pinch bolt. Wiser heads than mine are suggesting that I use leaded steel for the liner, and as I have a piece of 12L14 left over from my last engine I will probably use it for the liner with cast iron for the piston.  My course of "step by step" actions will be to first make the cast iron piston, turning the outer diameter of the piston to about .001" to .002" oversize from my desired 24 mm (0.945"). I will then set the piston aside.  I next machine the outside diameter of the piece of material for the liner to ensure it's roundness over the full length, including an inch or more to be held in the chuck jaws. Next I will bore the liner and chucking stub to about .0015" to .0001 undersize and then turn the outer diameter to finished size, turn the "lip" at the top of the liner to finished size, and still leave the liner attached to the "chucking stub" held in the lathe. Then over to the rotary table to cut the ports and sparkplug hole in the sides with the mill. Then back over to the lathe to lap the inside bore to exact size, using a lap mounted in the lathe and the cylinder liner in my hand (I try for a tighter fit at the top of the liner than at the bottom--this is sort of a "by feel" thing.). Now, assuming the cylinder liner is exactly finished to "On size", I put the chucking stub end of it back into the lathe. No farther machining operations will be carried out on the liner, except to part it off from the chucking stub after the piston is fitted. I then use the external lapping tool on the piston by hand, and bring the piston down to a point where it will just begin entering the bottom end of the cylinder liner. At this point I attach a T handle to the piston, using a temporary brass "wrist pin" and using a solution of very little fine diamond paste with a lot of kerosene, lathe not running, I wring the piston in and out of the cylinder by hand, untill I feel it enter freely up as far as the exhaust ports ,then with increasingly more friction as it reaches top dead center in the cylinder. This can be adjusted by just how much lapping I do of the piston into the cylinder. When I am happy with the fit, I then part off the liner from it's chucking stub.---Have I got the sequence right???---Brian

Offline Jasonb

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Re: Old School Barstock 2 Stroke
« Reply #27 on: February 17, 2016, 06:24:47 PM »
I'd not bother to bore the chucking stub, why have an extra long overhang on the boring bar that is more likely to flex and give a tapered bore. Once you have cut your ports part it off and then lap it.

Also not keen on diamond as it can get embedded in the metal, you should have Lee Valley woodworking in your neck of the woods they sell Vertas lapping powder.

Model engine builder had a design for the adjustable external hones but I use the brass type Ramon shows

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #28 on: February 17, 2016, 07:08:48 PM »
I thought that it made more sense to bore all the way thru the chucking stub to prevent boring and lapping into a blind hole. Of course, I could always put an oversize counterbore in the other end of the chucking stub first, so that my real boring and lapping just ran out into the counterbore, right?

Offline Brian Rupnow

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Re: Old School Barstock 2 Stroke
« Reply #29 on: February 17, 2016, 08:00:13 PM »
These two parts are going to be the most critical parts on the engine, in terms of me being able to make them well enough to give sufficient compression for an engine to run, so this is where I am going to start. Contrary to what I said earlier, I haven't made them yet, so don't bother to copy them. They may change. I will post a download link to all the drawings when the engine is finished and running.---Brian


 

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