A few questions on Boll Aero 18 plans abbreviations/notes.

[Max_Power]

Hi Guys, I've been lurking around here a bit , But this is my first post. I am building a Boll Aero 18 ...Actually I'm building 3 at once. ;D I have all the stock cut and a few of the parts have partial machining. I am waiting to get my fasteners/hardware and clear up some confusions before I move on.

I have a few questions on reading the drawings. Is there a "key" anywhere (I'm sure it changes by artist and region and is hard to be definitive)

1. Several holes like the horizontal hole through the crankcase for the front nose and backplate are noted: "
2 x n0.890 x THR" Why does it say "2x" as it seems to me like a .890 through hole is wanted?

2.What does "PCD" mean? I'm sure it is the definition of a bolt circle, But I'm confused.

3. There are handfull of parts that have big blue arrows. lines that come out of the part on opposite sides then make a 90 degree turn and the big arrows pointing in some direction. Examples are the piston and connecting rod.

$. does anyone have any 3d pictures or graphics of the parts of the engine ? "orthographic projection??" etc so it is easier to visualize the parts while I am getting used to reading the plans. Or even some photagraphs of a Boll Aero disassembled and made to plan specifications ?

Thanks in advance guys, Todd

 

[steamer]

2X in front of the feature call out means 2 places.....I don't have the print in front of me, but look at it from that perspective


PCD is the abbreviation for Pitch Circle Diameter or as you stated it's the same as Bolt Circle Diameter.


Dave

 

[Max_Power]

Thanks for clearing up the PCD deal. I figured it was just diameter, But easier to ask than start over . I'm still really confused by the 2x thing. Could it mean they want me to start the hole from each side and let it meet in the middle? Here is a link to the drawings. http://modelenginenews.org/plans/BollAero18.pdf Page 2 is the crankcase drawing I'm talking about, But it occurs several times in the plans on different parts where there is clearly only 1 hole. Thanks, Todd

 

[steamer]

2X or 2 Places would depend on the actual drawing.

It could mean 2 holes in two different locations or if it's a bore, it could mean there are two concentric diameters on either side of the part.....need to see the print to tell.

Dave

 

[Leucetius]

From my point of view the "2x" is unnessesary... It's clearly stated as a "trough" hole and there is only one of its kind - so forget about it.

The blue arrows with the character belong to the section view the arrows are pointing from (for example page 6; the section view A is at the wrong side but that's a minor error). You may read http://158.132.153.100/Doc/DRG_3.pdf for advanced version as steped section or so.

 

[steamer]

Hi Leucetius,

Apparently, I need to learn how to read a print?

The rules apply if the person drawing the print follows them,,,,,like abbreviating THROUGH with THR, is not necessarily obvious to me....but I'll leave it to the experts

Dave

 

[Max_Power]

Steamer , perhaps it isn't working or was missed as I edited it in about 10 seconds after the posting, But there is a link to the drawings in my previous post if seeing them would help. Thanks in advance. Todd

 

[steamer]

Thanks Max...I think your talking about the view in the block that states.

2X (diam symbol)0.890 (depth symbol) THRU.

The bore is a through bore interupted by the cylinder spigot.

I believe the author did this because of the interuption in the bore....there are two 0.890 diameters one on either face seperated by a central bore.

IMHO.....
It would be best stated on the print 0.890 THRU....first choice.
As stated previously, I also think the 2X is not necessary.

Dave

 

[steamer]

Page 7 , Cylinder Head.

If those are the big blue arrows your talking about, they are section lines

They show where the section view is taken. Think of it as where the part was sawn. The arrows point in the direction of which the section view represents...in this case they are pointing up. In this case, it is telling the reader that the section is viewed looking at the upper cut section of the cylinder head.

Dave

 

[Max_Power]

Thanks Dave! , I was figuring it out slowly but the explanation of the cut lines helps a lot! Now I can get some more work done on other parts while I'm waiting on fasteners and a bottoming tap to arrrive. Todd

 

[steamer]

Actually, I think the projection is screwed up on that....or it's first angle...don't know which

But I think you get the idea.

Dave

 

[samuel10]

Hi the drawing dosen't tell you how deep the grooves are next to the fins in the cylinder head.

 

[lensman57]

Hi,

You have already been told about pcd, 2X something and others. As for the sections, big blue lines with arrows, the best bet is to read about sections in engineering drawings as these could be quite complicated. Sections are usually used to clear up a drawing as dotted and hidden lines are sometimes quite difficult to imagine.

Regards,

A.G

 

[Leucetius]

From the look of it, I'd guess 0.275 depth. The wall of the cylinder head has the same thickness as the fins (measured by eyeball). that means bore + 2 x wall thickness = ground of fins = 0.7 + 2*0.05 = 0.8.
The groove's depth is (outer diameter - ground of fins) / 2 = (1.35 - 0.8) / 2 = 0.275.

Beside that if a dimension isn't given, it means a) it is shown at an other part / view (not the case here) or b) it isn't relevant.
As the engine probably won't run long times, the fins aren't crucial. So the depth depends on two things: leave enough metal around the bore and give place for the head screws.

Bottom line: the plans aren't the best in terms of readability for someone who is new to this.

 

[Ramon]

Hi 'Max'

I read this for the first time today and took a look at the drawings on MEN - your link BTW brings me back onto HMEM not MEN. I replied but when I tried to post it it told me I had to register before I could post - I lost the lot
Hopefully this won't happen again tonight.


Steamer and others have explained the 'THR' - 'through' but I too am a mite baffled by the '2 X'.
I see it's also on the bearing housing - 2 X .313 and on the crankshaft web/disc - '2 x .156' as well. I'm not familiar with the 'drill down' symbol either so maybe this is a part of this type of dimension/designation. As others have said just ignore it and machine it through.

FWIW - The drawings that I could find on MEN show several crankshafts all of which have a hole drilled down from the disc end and a through hole out into a relief turned in the shaft. As someone well familiar with diesels I cannot understand the reasoning for this as the engine as drawn is a sideport induction. Even if there is a front induction version you would not relieve the shaft in this area as this would render the timing useless. The only thing I can think of is that it may be a means of getting lubrication to the shaft but if so this method is to my mind totally unneccessary and a plain shaft will be much easier to turn and fit without these extra machining ops. The fuel that will find it's way under case pressure between the shaft and bearing will be more than adequate to lubricate the shaft.

Although I have never made one the Boll Aero is a nice little engine that has given many builders lots of satisfaction. These observations are not a criticism of the design just something to point out.

I wish you luck with your project - any other questions you may have just ask I'm sure you'll get lot's of help

Regards - Ramon

 

[Ramon]

Hi again, just re -read all the posts and took another look at the drawings - I see Ron Chernich drew them and his work is always excellent. I see however that where required (though not everywhere) he calls out for multiple holes on most parts eg .145 (4 places) (my dim) as distinct from the mysterious '2 X'

I notice the through holes for exhaust and transfer on the cylinder are just called out by diameter - ie no 2 X and neither is the bolt hole on the end view of the bearing housing (top right view). Leads me to think this 2 X may just be a typo

Something else Todd - hope I'm not teaching granny here but a little tip - when you do the cylinder heads you will find it much easier to debur the holes in the fins if you are able to put the holes in first before cutting the fins - the burrs caused by turning and left in the holes are much easier to remove than the other way round.

Regards - Ramon

 

[waynes world]

how i read it from his plan is ; he is giving you the dimensions of the crank case bore through x2 same both ends as in dimensions given. does that make sence.

 

[gus]

From the look of it, I'd guess 0.275 depth. The wall of the cylinder head has the same thickness as the fins (measured by eyeball). that means bore + 2 x wall thickness = ground of fins = 0.7 + 2*0.05 = 0.8.
The groove's depth is (outer diameter - ground of fins) / 2 = (1.35 - 0.8) / 2 = 0.275.

Beside that if a dimension isn't given, it means a) it is shown at an other part / view (not the case here) or b) it isn't relevant.
As the engine probably won't run long times, the fins aren't crucial. So the depth depends on two things: leave enough metal around the bore and give place for the head screws.

Bottom line: the plans aren't the best in terms of readability for someone who is new to this.

You are correct. I did build this engine and there were missing dimensions which you have to figure out.

 

[gus]

It was my first attempt. I chickened as I have no experience with honing the main piston,compression cap and the sleeve. Plan to restart. There are some fits which are very critical and unforgiving.The piston and sleeve fit.The compression cap.The shaft and bush fit.
I kept the engine as collection item.See foto.