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V-Twin 100cc Design & Build

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Craig Booth 105/08/2019 21:24:52
77 forum posts
133 photos

on to another relatively simple item. The prop thrust.

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Turned on lathe with counter bore. Reversed in lathe to add 0.5mm lip so only in contact with inner race of bearing.

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onto the mill to blind drill for M5 tapping holes

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moved onto side to drill thru for M6 grub screw tappings (both sides) which will marry with flats on the crankshaft.

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Graham Williams 1205/08/2019 22:51:54
25 forum posts

Very nice parts Craig.....

Graham

Emgee06/08/2019 09:16:04
1146 forum posts
206 photos

Hi Craig, what is the purpose of the recess in the front face of the prop driver ? I would have thought you need as much driver to shaft contact as possible with the method of fixing the drive to the shaft, also increased mounting face area for the prop, IMO a key would offer more security in operation and if also on a taper ensure concentricity of the drive system.

Emgee

Craig Booth 106/08/2019 21:04:08
77 forum posts
133 photos
Posted by Emgee on 06/08/2019 09:16:04:

Hi Craig, what is the purpose of the recess in the front face of the prop driver ? I would have thought you need as much driver to shaft contact as possible with the method of fixing the drive to the shaft, also increased mounting face area for the prop, IMO a key would offer more security in operation and if also on a taper ensure concentricity of the drive system.

Emgee

Hi Emgee, the recess is for the retaining nut which holds the prop driver to the shaft, the grub screws stop the rotation. Your'e right, a key would be the correct method but at the moment that is outside my experience and skill. The key and retaining nut seems to be the way most manufactured RC plane engines of this capacity appear to be fixed. I can image that this may be a part I may need to remake later in the build. Thanks for the comments.

Craig Booth 110/08/2019 21:09:37
77 forum posts
133 photos

This weekend I worked on the crankcase. Started with a big block of aluminium 76x76x65 in the lathe off centred and bored the main crank axis hole. All the other work was carried out in the mill.

The edge chamfers I will do later once the cylinder bodies are located. Now I just have 49 M3 holes to tap sad

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Craig Booth 114/08/2019 21:16:18
77 forum posts
133 photos

I didn't get any photos but when I had the stock in the lathe for the cylinders, I also parted off the 2 cylinder heads after cutting the fins. Being the same diameter it was easier to do while the stock was aligned.

Then moved to the mill to drill and counter bore the mounting holes (M4 bolts), and the 2 central holes which will be used to fix the rocker bracket. These are M3 threaded, but looking at them now I may increase to M4.

All the mounting holes are asymetric due to clearances needed on inlet and oulet holes.

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Next I made a basic block to hold the head while the other operations, circlular on one side to match the head, and square on the reverse to hold it in the vice and small rotary table I have.

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Fixed in the vice at 15degrees off vertical to drill the 7/32 hole for the sparkplug, tapped at 1/4-32, and counterbored to 12mm for plug wrench clearance.

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Moved to vertical in the vice and used 2mm slitting saw to cut fins in the top

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Then back to 15 degrees to chamfer the top edge to give plug lead clearance.

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Emgee14/08/2019 22:17:06
1146 forum posts
206 photos

Nice looking fins Craig, all look very crisp.

Emgee

Craig Booth 117/08/2019 20:39:08
77 forum posts
133 photos

more work on the head today, but first needed to get the rocker support started as I wanted this in place when I drilled the holes in the cylinder head for the valve sleeves so I would get perfect alignment.

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Once valve sleeve holes where drilled, fixed the head to the rotary table to mill the flats for the inlet/exhaust ports and to drill the ports.

These ports will need to be re-drilled once the colphos valves sleeves are in place, but the head will need to be anodised first and this cannot be done with any other types of metal present.

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JasonB17/08/2019 20:44:26
avatar
Moderator
15726 forum posts
1644 photos
1 articles

It's coming along nicely Craig and just goes to show you can hold milling cutters in a drill chuckdevil

Craig Booth 117/08/2019 20:47:27
77 forum posts
133 photos
Posted by JasonB on 17/08/2019 20:44:26:

It's coming along nicely Craig and just goes to show you can hold milling cutters in a drill chuckdevil

Ignorance is bliss. I guess as a newbie I can get away with it..wink

I presume now that you've hinted that the milling bit should be held in a collet instead for better accurancy?

JasonB18/08/2019 06:53:34
avatar
Moderator
15726 forum posts
1644 photos
1 articles

It is not just accuracy, the main reason is that a drill chuck does not hold the cutter very securely particularly when side load is applied and there is a risk of it moving. If you are lucky it will just ride up and not cut but due to the angle of the helix that the flutes follow the cutter is being pulled down when cutting, it would be a shame if this happened to a part that you had previously put a lot of work into.

I think we have all done it to start with or for the odd little cut where it's a faff to change from chuck to collet, (well at least I have) but would be worth investing in a collet chuck such as ER25 or 32 depending on what machine you have.

J

Craig Booth 118/08/2019 08:22:11
77 forum posts
133 photos
Posted by JasonB on 18/08/2019 06:53:34:

It is not just accuracy, the main reason is that a drill chuck does not hold the cutter very securely particularly when side load is applied and there is a risk of it moving. If you are lucky it will just ride up and not cut but due to the angle of the helix that the flutes follow the cutter is being pulled down when cutting, it would be a shame if this happened to a part that you had previously put a lot of work into.

I think we have all done it to start with or for the odd little cut where it's a faff to change from chuck to collet, (well at least I have) but would be worth investing in a collet chuck such as ER25 or 32 depending on what machine you have.

J

Thanks for the info Jason, that's something new i've learnt.

I do have a collet set that i use for the larger (16mm bit), but will look to use them for the smaller also.

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