Nalon Viper 2.5cc CI Engine

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Mechanicboy

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In my ED Seaotter has disc made of black plastic instead Tufnol. Maybe made of nylon or heat and wear resistant plastic material.
 

Billitmotors

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G’day Pat when I made my pair of Naylon Vipers I used Delrin for the discs. They worked brilliantly. I have used delrin on at least 6 other engines without any problems.
 

pat_pending

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I forgot to mention you can buy delrin in rod or sheet form as well. Also you don’t get the furry fibre on the cut edges.
G-day mate. Thanks for the tip. I had heard of people making gudgeon pin end caps out of it without issue so I assumed it must be OK as that is a MUCH hotter part of the engine. P
 

pat_pending

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Hi Pat just found these pics for you which may help









That should be self explanatory but if not just say. The green one is the oil filled nylon - though it worked I wouldn't recommend it

Tug
Hi Tug,

Just to be sure i understand (being a beginner muppet/novice) the sequence you are describing is as follows.

1) Rough out a piece of the Tufnol on a band saw.
2) Drill through
3) Mount on a mandrel in the lathe using that centre hole and make a generously oversized round.
4) Mount on rotary table locating on the outside of the round.
5) Mill the outer shape and holes to finished dimensions
6) Pop the round back in lathe and part off the disk valve (oversized e.g +1mm)
7) Mount the disk in the lathe in a pot chuck and face the back.

My worry is that the centre drilling and other operations are in different setups and some error might creep in to how perpendicular all the surfaces holes remain to that first hole where the pin goes. If i drilled that first hole undersize for the mandrel mounting then opened it up when the part is on the rotary table would that solve the problem?

Am I over thinking this?

Thanks and apologies for the noob questions.

Patrick
 

Ramon

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"Am I over thinking this"

Hi Pat, No, not at all, you're well on track with that procedure.

However as said before the most import thing is to get the running face (next to the backplate) as square to the bore as possible. The best way to ensure this is to take a very fine skim out of the bore when you skim the rear face in the pot chuck.

You can either make the central hole for the initial turning slightly smaller than finally required and bore the hole to suit the pin or, skim the bore slightly larger and make the pin diameter to suit the enlarged hole.

No apologies needed - for a self confessed 'muppet' you are doing remarkably well 👍

As Billit said you do get a 'furry' edge when machined but that's easily dealt with with a swipe of wet and dry paper.

Regards - Tug
 

pat_pending

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Hi, limited shed time as the garden has sprung into life and required attention / attacking with motorised implements. I did however get those valves done which turned out to be quite straightforward using the tips received in this thread so thanks again.

In the end I used Delrin just because it arrived first from eBay and turned out to be really easy to machine to a nice finish. Im happy with the result. Im assuming as everything (outer, face, holes, counterbores) were done in a single setup, everything should be nice and square. The facing of the rear side of the valve was done with the front side pressing against the back of the pot chuck so i'm thinking this will be parallel enough. I took measurements at the edges and they came out spot-on so I think I'm OK).

On to making some venturis spray bars and prop drivers next as gardening allows.

-P


IMG_0949.jpeg


Build was as follows.

Mount stock in the rotary table, face and turn the final OD with a 8mm 2-flute HSS mill.

IMG_0938.jpeg


Cut the profile, drill the pin hole, crankpin hole and countersink etc.

IMG_0945.jpeg


Part off the valve in the lathe with a decent bit of extra material for facing to size later.
IMG_0942.jpeg


now mount in an aluminium pot chuck and skim to final with. With the first part i needed to remove, measure and re-mount a couple of times to get the with spot-on. Nice thing with this fixture is that since the flange on the pot chuck sits against the lathe chuck jaws, subsequent valves could just be mounted and faced at the cross-slide position left for the previous part.

IMG_0947.jpeg
 

pat_pending

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I managed to burgle a few hours today and had a go at those prop drivers. Loads of great advice out there but in the end I went for the modelenginenews.org approach which seemed to match my skill level/experience well. This is exactly how I made them for the BollAero although somehow, the previous set caused lass drama + less scrap in the bucket. Maybe last time was beginners luck? Im happy with the result but I think the final fit needs to be made with a prop tightened-up. At the moment I have left about 1mm space between the driver and the bearing but the brass collar isn't really gripping the shaft yet. Hoping to get lucky and this gap will close up perfectly. Else I'll just skim a bit more off the back of the driver so no issues there.

On reflection, I think the BollAero collars were easier to trial fit as they were really, really thin perhaps 0.1mm at the thin end of the taper. this meant that on a test fit you could push down and the assembly would grip immediately. Here, these things as specified are big old 'wedges' so this requires more force to contract around the shaft. Perhaps this will make subsequent removal easier?..

Anyway, heres how I made em

Turn and knurl the prop driver blanks including the prop nut recess. I took the decision to relieve the edge a bit so any burrs created by plunge knurling wouldn't spread past the edge both inner/outer. I needed a snug fit into the pot chuck later so wanted to avoid lots of deburr/emery papering.


IMG_0920.jpeg


IMG_0921.jpeg


I realised i didn't actually bother taking a picture of the plunge knurling but standard stuff. Lots of WD40 and a brush to wipe the chips away as soon as they start clogging the wheel.


IMG_0924.jpeg


Next up the cross-slide was turned to 10 degrees and a taper was cut in some tool steel.

IMG_0929.jpeg


Next the brass collars were cut at the exact same cross-slide setting.


IMG_0926.jpeg


The tool steel was cut away for a 'smidge' under the centre line, hardened and tempered.




IMG_0930.jpeg


The bits now ready for final seating.

IMG_0957.jpeg

Drivers now reversed and mounted in a pot chuck . The taper was expanded out with the 'D' bit reamer and lots of test fitting,

IMG_0956.jpeg


Fit too loose for the finished article but will fine tune when I've been able to tighten everything up properly. Also the bearing sits a tiny bit proud to the crank case. Once the prop is tightened up and everything is sitting properly I'll take a call on whether to stick the crankshaft back between centres snd skim the bit that the bearing sits on. Easy operation but would be a pain in the a*** to break something that late in the game.
 
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pat_pending

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Hi Tim, that was the one photo i forgot to take as I was too in the 'zone' dusting away swarf etc. It was a straight knurling wheel (eBay Chinese variety) plunged directly into the face of the driver. I counted micrometer marks and pushed the wheel in 0.8mm with lashings of WD40 which seemed plenty for a deep knurl.

-P
 

Ramon

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Hi Pat - further to your PM.

I make the tooling to cut the exhaust slots from either guage plate or silver steel.
I make this as a small cutter which attaches to a separate shank with a cap screw



The blank is turned first then the teeth cut in on the mill. The leading edge of the tooth is behind the centre line of the cutter to give positive rake to the tooth.

Each tooth is backed off by hand filing then the cutter is heat treated and quenched in oil. It is not tempered. This gives maximum hardness for the small use this will have. The teeth are finally finished by diamond file.


This is the one I made for the Eta engines - it did six liners without a hitch in EN1a free cutting steel. I prefer to do this dry as without flood coolant to get the swarf away any coolant applied by brush tends to make the swarf stick and crowd the cutter. Speed well down and feed to suit.



The three liners from the second batch. The transfer passages were not broached but drilled first then the passages milled and finally filed by hand to rectangular section. I made a very thin walled sleeve that registered on the top of the liner to reference the position of the top of the transfer 'cut off' inside the liner



Rather than answer by PM I though that may have interest for others.

Hope that helps you though

Regards - Tug
 

pat_pending

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Hi Pat - further to your PM.

I make the tooling to cut the exhaust slots from either guage plate or silver steel.
I make this as a small cutter which attaches to a separate shank with a cap screw



The blank is turned first then the teeth cut in on the mill. The leading edge of the tooth is behind the centre line of the cutter to give positive rake to the tooth.

Each tooth is backed off by hand filing then the cutter is heat treated and quenched in oil. It is not tempered. This gives maximum hardness for the small use this will have. The teeth are finally finished by diamond file.


This is the one I made for the Eta engines - it did six liners without a hitch in EN1a free cutting steel. I prefer to do this dry as without flood coolant to get the swarf away any coolant applied by brush tends to make the swarf stick and crowd the cutter. Speed well down and feed to suit.



The three liners from the second batch. The transfer passages were not broached but drilled first then the passages milled and finally filed by hand to rectangular section. I made a very thin walled sleeve that registered on the top of the liner to reference the position of the top of the transfer 'cut off' inside the liner



Rather than answer by PM I though that may have interest for others.

Hope that helps you though

Regards - Tug
Thanks Tug, that’s really helpful👍
.
I assume you made the cutters on the rotary table? I can picture making the leading edge of the tooth (noted what you said about positive rake above) I’m just not sure about cutting the back of the tooth. Possibly this is one of these operations that will be obvious once I get started. Looking closely at the profiles above it looks like each tooth has 3 cuts to it ( same endmill, rotary table advanced, different depth of cut). Is this how it was done?

thanks, P
 

Ramon

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Hi Pat -

I cut my teeth on the cutter shown using a dividing head with the embryo cutter shank horizontal but a rotary table will do the same if set up horizontaly. It can also be done vertically of course. Unfortunately I don't have any images of actually cutting the teeth but the depth of cut will set the rear face of the next tooth. Unless you draw it out first it's a matter of going round a few times increasing the depth until the proportions look right. Backing the teeth off so they dont rub is where the main attention needs to be. Bear in mind it's only the very outer edge that does the cutting but you don't want the cutter to rub. It's a good idea to radius the corners of the milling cutter used to cut the teeth so no stress point is created at the gullet

Tug
 

pat_pending

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OK great i think I'll draw it and maybe have a go on some wood/acrylic first to get my 'eye in'.

By 'backing off' I assume you are referring to the shape i've highlighted red below?



-P

Screenshot 2021-04-20 at 07.02.15.png
 

Ramon

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Hi Pat,

No, backing off is the reduction in thickness behind the edge you have in red (the silver areas). That red line is your cutting edge and that should be as close to as machined as possible. I think you are showing an early cutter made. This had each side tapered inwards on the lathe to give some clearance then the relief angles were filed. This worked but it meant that only the very tip of the teeth were controlling the finished dimension of the slot. These cutters need to do the slot to finished size in one go for best result.

The type shown before held horizontally and milled with the end of the cutter and not the side perform much better.

Heres a slightly better picture of doing an Oliver liner which may help


Regards - Tug
 

pat_pending

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Hi Pat,

No, backing off is the reduction in thickness behind the edge you have in red (the silver areas). That red line is your cutting edge and that should be as close to as machined as possible. I think you are showing an early cutter made. This had each side tapered inwards on the lathe to give some clearance then the relief angles were filed. This worked but it meant that only the very tip of the teeth were controlling the finished dimension of the slot. These cutters need to do the slot to finished size in one go for best result.

The type shown before held horizontally and milled with the end of the cutter and not the side perform much better.

Heres a slightly better picture of doing an Oliver liner which may help


Regards - Tug
Thanks Tug, that's really helpful. Will make a few experiments tomorrow to see how I get on. I happened to find a cutter of the exact dimensions in the US (50$ +26$ postage!) or made to order in the UK for £120. I think this really is one of those cases where there is no alternative :)

P
 

pat_pending

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Hi, I got a bit of time in the shed today and got started on the carburettor parts and the rotor pins. Will post pics of the carbs when all finished. I really am running out of bits to make before tackling those dreaded cylinder liners!

IMG_0971.jpeg


I tried the tempering using the hot sand method following Tug's ETA build thread. Mine went straw rather than black but perhaps thats because I was using D2 tool steel not silver steel? Anyway, they worked out OK.

I used a bit of copper tube squashed down and tapped to hold the pins. This seemed to work a treat. Beware, the copper conducts the heat a LONG way up the tube and doesn't get cooled down through the quenching... Don't ask how I know. After the heating to what, in my opinion, looks like a cherry colour, I kept it there for about a minute then quenched in oil. I was carful to have the pin square to the oil to minimise distortion.

IMG_0968.jpeg


I then sieved some sand and heated it for a long time while stirring to get out any moisture (I'm sure the dog wont miss her food bowl :) ). The bowl was glowing red at the bottom and I must have heated for a goof 20 mins. Checking with the Maplin cheepo IR Thermometer, the sand was showing 320C and I couldn't get it any hotter.

At this point I stuck in the pins that had been cleaned and made shiny again on the top surface. I watched closely until the 'straw' colour came and went. i was hoping for that nice black Tug got on the ETAs but I think this was all i was going to get with the D2.



IMG_0970.jpeg
 

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777engman

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Hi, a bit more shed time today. I have finally found the parts I like making the least: Conrods.... or at least this is the first time I've done it and it still honing the technique. They turned out OK (accurate where it counts) but the profiling is still a bit iffy.

I used the approach detailed on modelenginenews.org linked below:


Anyway heres the build log.

It all started from a piece of Alumec 89 which Tug kindly let me have. This stuff is hard as nails and v difficult to saw! I shaped a block to +5mm oversize in all dimensions then drilled the big/little end holes ( -0.2mm for reaming later)

View attachment 124095



View attachment 124096
Next up I used a slitting saw to cut off slices of the conrod width + 0.5mm.

I then proceeded to surface the width to size and once finished, centre drill at the big end for turning between centres.



View attachment 124097

Once done i popped the blanks into the 4-jaw and turned with my first ever hand ground HSS tool with 45deg edge. Worked OK for first try but could use some practice. Felt pretty blunt. That Alumec turns great and gets really shiny. The only trouble is it's so hard that the burrs are a bl**dy nightmare to remove!


View attachment 124102

Next up I made a jig to profile the conrod ends. The brass disks are the desired final diameter of the ends.

View attachment 124099

Time for hours of hair-rasing machining with fingers just milimeters from the endmill.

View attachment 124100

All OK apart from one below that was snatched by the endmill and got destroyed. The Alumec killed the HSS endmill too! That is some strong stuff! Lesson learned: if its trying to snatch the part, tighten up the jig and take lighter cuts.

View attachment 124101

Anyway, here they are. They will work and look a lot better after some deburring.

View attachment 124103

On to some easier bits next. Think cylinder heatsink or prop drivers.

Bye for now,

Patrick
best to do this op with a rotary table, that never happens then, I've made several hundred con-rods and not had any of them do that. discovered the rotary table option after your experience happened to me once, nearly lost a thumb.
Regards
Dean
 

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