Building #52, Elmers RVTW

[cfellows]

Nice work, MB. When you use loctite, how close a fit is the hole to the shaft?

Chuck

 

[Metal Butcher]

Nice work, MB. When you use loctite, how close a fit is the hole to the shaft?

Chuck

Hi Chuck. I honestly can't accurately measure a 1/4" hole, but I used a .250" precision ground s.s. rod on this crank and reamed the holes with a .250" reamer which gave me a snug sliding fit. I usually get a light press fit, but it seems that on aluminum the reamers go just a little more over than on brass or steel. But I would venture to say the gap was less than .001" in this particular build up.

From what I understand Loctite will fill and seal a much larger gap, but a good close fit is nice for a good line up between the parts.

I see that you got back to the 4 cylinder build that you shelved last year. I was hoping that you would get back to it. I would like to build one along the same lines someday.

-MB

 

[Metal Butcher]

#39 I made the spring retaining 'screws' from standard 360 brass hex. I machined the three diameters using my simple DRO system. Its has adjustable rods that make contact with two fixed position 0-1" AGD group-2 dial indicators. The "Dial Readout" set up cost me less than $20 including a few scrap blocks of aluminum and the two steel rods.

#40 After I threaded them 1/4-40 I cut them off with a parting tool. The picture below shows the 'springs' and '3/16 ball' bearings that will press and hold the cylinders against the column. I'll be using .180 x .020 x .626 springs on hand. I got these from Enco (part # 240-0561). They are a smaller wire diameter, but longer than what's specified in the plans. If I notice any cylinder lift or leakage I can go up to the next (heavier) wire size.

#41 I made the 'cylinder retainer' as a build up of three parts. The two screw bosses were machined to a .3755 diameter by 3/8" long. Prior to cut off in the lathe they were tapped 1/4-40.

#42 I drilled and reamed the ends of the 'retainer' .375 for a light press fit, and assembled the three pieces with the addition of Loc-tite. The sides of the 'cylinder retainer were clearance drilled #32, and countersunk for the two 4-40 flat head screws that will hold it to the 'column'.

#43 I finished up the previously milled 'base' by drilling all the necessary holes. The four corner clearance holes were reduced to #32 drill for the 4-40 screws that will be used to mount the engine on a wooden base. I was puzzled by the 1/8" holes indicated in the plans. Maybe that's a correct size for wood screws?

I didn't get much done today. I got together with my biker buddies for our monthly breakfast-get-together. Were a tough old bunch of bad @ss bikers, that brake for squirrels and never go over the speed limit. :big:

-MB

 

[tel]

The 90 degree offset on the crank throw has me scratching my head. I keep thinking that maybe I should have changed it to 180. Any one have any thoughts on this?

If you do this the engine will not be self starting. With the cranks at 90° one side of one piston is always under steam admission, thus the vast majority of twin cylinder engines (and locomotives) are set up this way.

 

[Metal Butcher]

Thanks Tel. The self starting issue crossed my mind, but I wasn't sure. I dismissed the idea because my Open Column Twin is self starting and the crank pins are 180 degrees apart.

Could it be that the engine stops every time in an optimum position to self start?

I feel that the 90 degree offset will throw the engine off balance considerably. And it may have been a good idea to change that to 180 since my engine will probably never be used in a launch or other application where a self start is desirable.

-MB

 

[tel]

The balance is less of an issue than you might think, unless you are running at high speed. Elmer does try to address the issue somewhat by drilling that 3/16" hole through the centre crank web, between the two crank journals.

 

[Metal Butcher]

The balance is less of an issue than you might think, unless you are running at high speed. Elmer does try to address the issue somewhat by drilling that 3/16" hole through the centre crank web, between the two crank journals.

Since my crank shaft is made up of mostly light aluminum, I didn't bother with the drilled counter balance hole. However, I did think about drilling a 1/4" 'through hole' in the larger center crank disc opposite the piston rod journals, and installing a heavy brass rod with Loc-tite.

Its an idea that might have worked, but without weighing the parts to determine if it would work I decided against it.

-MB

 

[tel]

I don't think it would make a lot of difference either way. My crankshaft (when I get to it) will be all steel, but even so I don't think I'll bother with the hole.

 

[Metal Butcher]

#44 I didn't get much done. To much time was spent one choosing a chucks ,machining their back plates and cleaning up the mess along with a few other time consuming odds and ends.

I drilled the face ports on the 'column' using the drilling 'jig' provided in Elmer's plans. After spotting with the 1/16" drill, the 'jig' was removed to allow an easier escape for the chips. This method allows for a simple but precise way of locating the ports.

#45 To speed up the milling of the first two steps on the 'column', I cut out the excess with my band saw. Milling all of it out would have taken longer, and left an avalanche of aluminum chips to clean up.

#46 The final milling of the lower end of the 'column' will be done later and after the opening for the crankshaft is bored out.

#47 I prepared the 'column' for mounting in a four jaw chuck by placing tape where the face of the jaws will touch, and by gluing (spray adhesive) brass strips were the tips of the jaws will contact the workpiece tightly to hold it rigidly in place.

#48 The set-up below wouldn't work. The two side jaws contact each other on the first step of the jaws before contacting the work piece.

#49 The same set-up as the picture above, just a different camera angle to show the problem. Only two jaws are in contact with the work piece. It doesn't seem safe to proceed with the drilling and subsequent borring.

#50 By reversing three of the jaws to their inside configuration I was able to reach the work piece on all four sides. This leaves one jaw in its outside configuration.

#51 The picture below is the same set-up as picture #50, just a different camera angle.

I'm afraid to start boring out the opening by drilling a 1/2" starter hole.
With the face of only one jaw contacting the work piece (from behind) on a perpendicular plane to the spindle axis, There is a serious concern that the unsupported work piece could shift backwards.

I'm at a stand still with this set up and can't bring myself to start drilling.

-MB

 

[mklotz]

Two remarks...

Think of making yourself a spider to go behind the workpiece. An appropriately sized slice of aluminum irrigation pipe or similar cut to the distance between the back of the workpiece and the front of the chuck should do the trick. You can (temporarily) glue it to the workpiece for peace of mind but, since it's trapped by the four jaws, it can't really go anywhere.

If you decide to not use a spider, this may be one of the few occasions where step drilling is a good idea. By drilling in small increments you will minimize the force exerted on the workpiece.

Personally, I would make the spider. If you do, save it in a box labeled "spiders". You'll probably use it again in the future and you'll make more spiders during your career.

 

[Metal Butcher]

Hi Marv. My senses tell me that the spider is probably the safest way to go. It would however be totally custom to this odd offset piece, I think.

I thought about plunging in the starter hole with an end mill, and stopping periodically to check for a shift in the work piece.

I need to take another look at this situation before making any decision I might regret.

Thanks.

-MB

 

[mklotz]

It will take you probably 15 minutes to make the spider. How long will it take to remake the engine standard? Even if you decide to throw it away after using it, it's still worth making it for the insurance value.

 

[Metal Butcher]

It will take you probably 15 minutes to make the spider. How long will it take to remake the engine standard? Even if you decide to throw it away after using it, it's still worth making it for the insurance value.

I agree with you on all points. And I would recommend that any one facing this situation do exactly what you recommended.

That 4-jaw chuck just opened up a whole new dimension. No need for me to get creative on parts that need to be machined in a four jaw chuck. :big:

Thanks again.

-MB

 

[1hand]

MB;

Couple Questions for ya.........Do you see a real need for the 4" 4jaw with having the 6"?
All I have is the fine one that came with my lathe. Now with starting my build, looks like it could really come in handy.

Next, I see that you had to make a few solder joints, and am wondering what sort of torch you use?

Oh by the way, Nice job!!

Matt

 

[Metal Butcher]

I wasn't sure that the 4" would be adequate, and guess what! My first time use of a four jaw required the 6". The 6" is really big and heavy, so I'll use the 4" when that's all I need. I just checked the 4" and it will close down on two sides of a 1/8" rod, and with all four on a 3/16" rod. The valve lever on my current build is 1/8" x 3/16" and hopefully it will close down on it. If not the 1/8" sides will need shimming. I can't check the 6" at the moment since its tied up till tomorrow, but I believe the larger jaws don't close down as small as the 4".

If you get one, than I would say the 6" is the way to go. If the quality is acceptable you can always order the additional smaller 4" if you feel a need. There is no discount on shipping since the sellers can't throw it in the same package and add a pound or two in shipping cost to you bill.

This is assuming the 'Shars' brand is your choice. There's a lot of brands and sellers out there to choose from.

Having a usable independent four jaw chuck is really a must, in my opinion.

-MB

 

[1hand]

Did you get your 4 jaws from that place in OH?

 

[Metal Butcher]

Sorry I forgot to mention that I use a standard Bernzomatic propane torch for soft 'Soldering'. I have been successful using it to 'silver braze' on very small pieces that will get 'red' hot. Although for 'silver brazing' an oxygen/acetylene setup is the way to go.

-MB

 

[Metal Butcher]

Did you get your 4 jaws from that place in OH?

Yes, Ohio was the way to go for me. Its a 'Shars', same as the other two sellers. Study the pictures closely. The shipping will be different for you because of the shipping point. Mine made a 35 mile trip across town in a UPS truck. No pick ups allowed. Most of these guys don't want to be bothered, or don't want anyone to see their Mickey Mouse operation. ;D

-MB

 

[1hand]

What you think of this Idea...........Getting a 6" 4jaw and instead of the 4" get a 3" 5c 4jaw chuck. Being I have the 5c on the lathe now. Would the 3" be useless do to its size for most of the Elmer's engines? I thought it would be nice for them lathe to mill transfers. I already have a 5c Indexer for the mill. Wouldn't have to re chuck and would save me an additional back plate to make.

 

[1hand]

Or.................... get the cheap 4" 4jaw and the 4" 5c mounting blank from my buddy there at CDCO for $36 and be set.