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Member postings for Craig Booth 1

Here is a list of all the postings Craig Booth 1 has made in our forums. Click on a thread name to jump to the thread.

Thread: V-Twin 100cc Design & Build
18/08/2019 08:22:11
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.


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.

17/08/2019 20:47:27
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?

17/08/2019 20:39:08

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.




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.





14/08/2019 21:16:18

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.


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.



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.


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


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



10/08/2019 21:09:37

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










06/08/2019 21:04:08
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.


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.

05/08/2019 21:24:52

on to another relatively simple item. The prop thrust.


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



onto the mill to blind drill for M5 tapping holes



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



05/08/2019 21:14:41

good thing my lathe has a replicator button...wink going to be needing that a lot on this build



30/07/2019 06:45:02
Posted by Graham Williams 12 on 29/07/2019 22:10:30:

Hi Craig, this is a lovely project and superb CAD drawings, especially the fully rendered 3D images. As an engineer and keen RC aircraft fan I'm looking forward to seeing this running and flying. Do you use Inventor in a professional capacity?


Thanks Graham, I am an engineer by trade but in a different field (building services - heating,cooling, ventilation, sustainability etc). I don't use Inventor at work but was already familiar with the standard AutoCAD software so it did not take long to teach myself Inventor and is it relatively intuitive


28/07/2019 19:07:41

move to the mill to drill the bottom set of holes for bolting to crankcase and milling the octagon faces.



all that remains are the top set of holes, but think I'll leave these until later as they are non-symetrical and also mirrored for each cylinder head bolt pattern.


28/07/2019 12:30:45

parted off overlength, reversed in chuck and faced off to length.



27/07/2019 21:50:13
Posted by Rockingdodge on 27/07/2019 15:54:01:

What type and size plane are you building Craig?


Rodger, I'm drawing up plans and have it half cut out for a 1920's style racer. Its a mix hybrid between a Gee Bee R3 and Chuck Gratners Riley B design. Wingspan 100", target weight around 14-15kg

27/07/2019 13:08:08

started to make some chips. Cylinder No.1


2.5" HE30 barstock, machined down to 62.5mm OD. Fins are 1mm width with 2mm space, 7.5mm deep.







20/07/2019 19:03:26
Posted by JasonB on 20/07/2019 08:55:35:

You can get some much neater and nicer looking plug tops than those Rcexl ones

yeah, they are a bit plain, but what came with the unit. Will consider changing them but that's a long way down the track.

20/07/2019 08:18:25

Slower progress now that I'm back at work.

Checked the counter bore depth needed for the sparkplug. I am using a small sparkplug type (same thread as a glow plug 1/4x32).


Also realised that the spark lead would foul on the edge of the cylinder so have reduced the spark plug angle to 15deg and also chamfered the fins to give clearance.



12/07/2019 21:38:56
Posted by JasonB on 12/07/2019 12:33:50:

Craig, unless you particularly want chromed exhaust stubs you could solder them up from stainless steel and polish to your desired finish.

Jason, have never tried silver soldering stainless, but could be a better idea than having to rely on external chrome plating. Also like to try something new.

12/07/2019 10:28:40

To give a rough idea how the engine will fit in the cowl. The exhaust manifold will wrap around the outside of the cowl curved to the rear.

Ignore the outlet on the other side, I now need to mirror both the cylinder head and cylinder for that side.


11/07/2019 21:08:04

Some more work on the head to change the inlet/exhaust connection. I now have a plate connection which will allow me to easily make the manifolds that will be need to be bent to shape to suit the cowl. Manifold will be copper, silver soldered to flange. The lot can then be chromed.




11/07/2019 16:47:10
Posted by Niels Abildgaard on 10/07/2019 08:29:57:

I think You need to reserve more space in crankcase for crank,counterweigth and conrod big-ends.

The crank shown from a leaf-blower engine balances all rotating and half reciprocatory forces.

To achive primary perfect massbalance i a 90 degree V-twin You shall balance all rotary and one reciprocatory totaly.

This means that Your crank will be two times as voluminous relative to piston as shown on picture.

Hi Niels, yes balance will be via all rotary and 2 times half reciprocating mass.I'm pretty sure I have enough space to do this as there will also be the rear crank web. Of course it will not be based on volume as you note above but mass, with the steel of the crank web having a greater mass per volume than the lighter mass of the piston.

Another good think about Autodesk Inventor is that it calculates mass and centre of gravity of all parts based on material, so I will be able to use this rather than trial and error balancing.


11/07/2019 13:03:12

Cylinder head altered a little, increased height by 2mm which allows better sleeve support and also slightly larger fins.


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