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Dec 02, 2019, 05:39 PM
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JackHiner's Avatar

Drone BB Diesels


I have four Drone BB diesels. I use the Aerodyne VC head for these diesels with two mods. A compression locking lever to hold the compression setting. And after two "O" ring contra piston failures I went with two "O" rings. Also I have used a machined intake restriction for SAM Texaco event. The best runner looks the worst with a cylinder cooling fin chipped. On a good day this one can turn an APC Sport 13/7 prop at 7,000 RPM. Has touched 7,100 RPM but not held for long. I have a custom made muffler some where. Now I need to find someone to modify one with and .15 size RC carb. Jack Hiner
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Dec 02, 2019, 07:15 PM
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Maybe one should go to a "proper" contra piston and forget the "O" rings Jack . I've never found a reason to use this type of contra piston setup , it's far easier to set up a properly fitted piston to my mind . They can be made blow back or push / pull quite easily .
Dec 02, 2019, 10:43 PM
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earlwb's Avatar
I happen to have three Drone .29 Diesels too. Both the plain bearing and BB versions. I did manage to get a glow head as well as adjustable diesel head from someone in Italy, amazingly enough. I put a RC throttle on a plain bearing version using an adapter I made for it. Granted a throttle doesn't really get to throttle much with it being a low RPM engine. The little Fox .15 mufflers do seem to fit fairly well on the engines too. I just use a screw on clamp with it.
Last edited by earlwb; Dec 02, 2019 at 10:43 PM. Reason: typo
Dec 02, 2019, 10:47 PM
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Now then Davis Diesel Development made a mold and ran off a limited number of Drone Diesel crankcases. I got one of the units, but I haven't done anything with it yet. Mainly because I haven't figured out how to drill the three small holes for the crankcase to front end on it. Those holes are small, long or deep and there isn't much material on the crankcase in case of drifting while drilling.
Last edited by earlwb; Dec 02, 2019 at 10:49 PM. Reason: add picture
Dec 02, 2019, 11:14 PM
DJS Johnny
johnshannon's Avatar
Quote:
Originally Posted by earlwb
Now then Davis Diesel Development made a mold and ran off a limited number of Drone Diesel crankcases. I got one of the units, but I haven't done anything with it yet. Mainly because I haven't figured out how to drill the three small holes for the crankcase to front end on it. Those holes are small, long or deep and there isn't much material on the crankcase in case of drifting while drilling.
Earl,

One method I have used in a tight space with a deep hole like you described is to use a center cutting endmill. Pick one a little smaller than the needed tap drill hole. It will go straight without drifting. Take your time to only go a little at a time and retract to clear out the chips. Then size the hole with the tap drill.

Johnny
Dec 03, 2019, 01:56 AM
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krafty's Avatar
Johnny, forgive my lack of knowledge, but what is a centre cutting end mill ? Is that what I know as a slot mill, or something different that I ought to know about?
Ken
Dec 03, 2019, 03:39 AM
I'm a balsa butcher
A slot mill (slot drill) has 2 flutes. An endmill has 4 or more flutes. A unimill has 3 flutes.
Dec 03, 2019, 05:57 AM
Ted Luginbuhl
ukanduit's Avatar
https://www.machiningcloud.com/wp-co...pplication.pdf
Look at page 7 for the center vs non center explanantion.
Basically plunge vs side milling...

Another approach to "high aspect ratio" holes like on the Drone would be to use a small "gun drill". You can make these in the home shop by forgoing the coolant hole in the the tool and just frequently clear the hole of chips. The coolant hole is more of a aid to speed things up and not essential to the action of the tool. I attach a pic of the basic idea. The point offset and flute design are keys to the drill's ability to self correct.

But I like Johnny's center cutting end mill suggestion when you have the right size end mill.

Image from "Rifling Machines And Methods" by Clifford F. LaBounty
Last edited by ukanduit; Dec 03, 2019 at 06:14 AM.
Dec 03, 2019, 09:23 AM
DJS Johnny
johnshannon's Avatar
Quote:
Originally Posted by krafty
Johnny, forgive my lack of knowledge, but what is a centre cutting end mill ? Is that what I know as a slot mill, or something different that I ought to know about?
Ken
Quote:
Originally Posted by udlman
A slot mill (slot drill) has 2 flutes. An endmill has 4 or more flutes. A unimill has 3 flutes.
Quote:
Originally Posted by ukanduit
Look at page 7 for the center vs non center explanantion.
Basically plunge vs side milling...
Another approach to "high aspect ratio" holes like on the Drone would be to use a small "gun drill".
All great comments! Yes, a center cutting end mill can be plunged straight in. It will cut a nice hole without drifting. It also side cuts great. I usually buy the center cutting (actually steal from Dub) so no matter I will have the right one. It acts just like a boring bar in a boring head.

I did not know there were names for different flute count. Interesting.

And finally, a gun drill is the greatest. However, they are more expensive. There were applications at work where they were used, but usually for much higher aspect ratio holes than in model engine work.

Two other items of interest on end mills. This is just from my own experience. If you do not need a very sharp corner, get one with a small corner radius. I have no idea why, but they seem to stay sharp longer. And, you can make a really nice micro boring bar from a small dia end mill. Just take the cutting edge off one flute and the side cutting edge off the other except the last 1/16 in or so. Much less cost.

Keep in mind I am in no way a machinist, but I have hacked out a few parts in my time. I know there are real machinists here who might want to give some tips.

Johnny
Dec 03, 2019, 01:58 PM
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krafty's Avatar
Quote:
Originally Posted by udlman
A slot mill (slot drill) has 2 flutes. An endmill has 4 or more flutes. A unimill has 3 flutes.
I know that, but that does not answer my question.
Johnny mentioned a centre cutting end mill, and I asked if that is the same thing as a slot mill, or is it some cutter that I have not come across.
Life is full of new discoveries, for instance after 60 years of engineering I have just discovered that often I use a centre drill when I should be using a spotting drill. That passed me by entirely. I am always willing to learn even at my advanced ed age.
It appears that Johnny's cutter is my slot drill/mill.
The problem that I see in using a small slot drill to poke holes right through the Drone casting, is that small diameter slot drills in my shop would not be long enough. I would just drill undersize at first with a newly properly sharpened ordinary drill and load of white spirit, and all should be well.
Ken
Dec 03, 2019, 03:56 PM
DJS Johnny
johnshannon's Avatar
Quote:
Originally Posted by krafty
I know that, but that does not answer my question.
Johnny mentioned a centre cutting end mill, and I asked if that is the same thing as a slot mill, or is it some cutter that I have not come across.
Life is full of new discoveries, for instance after 60 years of engineering I have just discovered that often I use a centre drill when I should be using a spotting drill. That passed me by entirely. I am always willing to learn even at my advanced ed age.
It appears that Johnny's cutter is my slot drill/mill.
The problem that I see in using a small slot drill to poke holes right through the Drone casting, is that small diameter slot drills in my shop would not be long enough. I would just drill undersize at first with a newly properly sharpened ordinary drill and load of white spirit, and all should be well.
Ken
Ken,

Sorry I did not answer your question. Online and in the tool catalogs I have there are a million end mills listed. Typical page below. Some are listed as center cutting. This is the type I use because they can be plunged into the part and make a very straight, round, undrifted hole that is flat at the bottom. I also get solid carbide because they last longer, don't break as easily and don't flex as much. I also get double ended because you get two for less than the price of one. I paint the end that finally wears our red. I also get ones for aluminum that are 2 flutes as I machine aluminum more than anything else and they clear the chips better. They will cut steel just fine as long as you go slow.

I had never heard of a slot mill. When I searched the catalog it did find a few. I really don't know what their specialty is.

I did not know what a spotting drill was until Dub started using NC machines. They put a cone exactly as positioned and don't walk. I have not used a center drill in 30 years. They also are a great chamfer tool.

You can get center cutting end mills in tiny sizes. Then size with a tap drill. However, that casting looks like it has plenty of material to spot drill the location and use a brand new tap drill retracted often to clear the chips.

Johnny
Dec 03, 2019, 04:01 PM
DJS Johnny
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Forgot Picture


Forgot End Mill Page
Dec 03, 2019, 09:18 PM
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earlwb's Avatar
Thanks for the information. I appreciate it.
Dec 04, 2019, 02:47 AM
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krafty's Avatar
Thanks Johnny, good information as usual.
I guess that a slot drill or slot mill gets its name because it is the tool you would use to cut a closed ended slot like for a key way. You could not do that with a conventional end mill that was not centre cutting.
Ken
Dec 04, 2019, 06:22 AM
Ted Luginbuhl
ukanduit's Avatar
Quote:
Originally Posted by krafty
Thanks Johnny, good information as usual.
I guess that a slot drill or slot mill gets its name because it is the tool you would use to cut a closed ended slot like for a key way. You could not do that with a conventional end mill that was not centre cutting.
Ken
You can use a non- center cutting end mill to do that Ken. You would need to "ramp" it into the work as opposed to "plunging" in.

Ramping is simultaneous side cutting and plunging as the name implies.


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