Nalon Viper 2.5cc CI Engine

[Ramon]

Excellent link Ken, I do climb mill to eliminate burs but it does look like I've been doing it wrong for too long

Not quite so sure that would be the answer on thin workpieces but for blocks that really looks worth a try.

Tug

 

[pat_pending]

Have you seen the video by Joe Pie... on squaring blocks on the mill.
I found it helpful and I always do it this way.
Ken

hi Ken. Don't know how i missed your reply. Apologies! Thanks this is really helpful. The 'bad' way using the wire and then an engineers square that he referenced is of course exactly what I was doing LOL. I'll give this a try. I unfortunately converted my mill to CNC a few years ago (which I regret). These sort of 'just skim a bit off here and there' operations now take considerably longer! I'm getting faster at typing raw GCODE but still miss being able to do things by 'feel' as I do on the lathe.

Patrick

 

[Ramon]

Hi Patrick, Ken,

I tried this method on a slab of cast iron about 30 x 25 x 75mm this last week. Sawn on all four sides but gripable in a vise it proved a very viable and quick way of squaring up. Excellent idea and well worth passing on - thanks Ken.

Keep on tapping that G codeout

Tug

 

[pat_pending]

Hi All,

finally managed to get some quality shed time in over the weekend. Work has been too tiring to get any evening sessions in so slow progress at the moment. I had another crack at those front housings using the advice you all gave me and looks like success . I used the expanding mandrel with the 60deg cap screw which worked an absolute treat. It did really only take a tiny bit of force on the cap screw to get a tight grip.

I also managed to recover the other two housings using the Tug Insert and Loctite method which seems to have saved em. The bearings are in and they spin great + the housings seem really airtight too. All-around happy, some pics below. Is this two engine build turning into a 3 engine build?


Thanks again for all the tips. Onto those conrods next so hopefully i can pick up a bit of pace.

Patrick

Here's the mandrel. I finished the final size after slitting + de-burring to make sure everything was as true as possible and compensate for any runout on the 3JSC chuck.

Shim Lockited (is that a word?) in and cured for 24hrs. Ready to machine.

Good as new... and true!

Finishing / profiling operations on front-housing #3.

 

[Ramon]

Well done Patrick - looks like you are back on track. BTW an expanding mandrel should always be trued after slitting. They are certainly useable again but rarely run true so have to be re-trimmed for something smaller.

Regards - Tug

PS there's no k in Loctited

 

[pat_pending]

PS there's no k in Loctited

Typo fixed . Will recommend this verb is added to the dictionary

 

[jetstuff]

Is it possible to make the crankshaft in two pieces? (say.... silver steel shaft and EN24T web) and also the crankpin from a needle roller? I hate making the interrupted cut on the lathe,

thanks
john

 

[Ramon]

John,

All the 5cc diesels save one I have made so far have had a composite crank shaft as you describe but with a integral crankpin. The inner shaft is best made from a caphead screw. I use this as material not for the thread - that is screwcut when the entire shaft is finish turned. The pin area is first milled to a square section to minimise the period of interupted cutting on the lathe

If you check this thread - ST-32- about halfway down the page you'll see how I went about it

Needle rollers make fine pins but it has to be a good interference fit and a decent web thickness to work successfully.

Tug

 

[xpylonracer]

Jetstuff

I don't think silver steel is the best choice for the shaft, EN16T or EN24T throughout or do as Ramon does because he has proven his method beyond doubt.

 

[jetstuff]

Thanks chaps, I have just made a shaft to convert a PAW 15 to a twinshaft, using (what I bought as EN24T) , I get a horrible finish, even using power feed and very light cuts. The first one got the (threaded end) bent during production between centres, this one is a bit better (in the four jaw chuck) but not great....still got some learning to do!

 

[Richard Hed]

Is it possible to make the crankshaft in two pieces? (say.... silver steel shaft and EN24T web) and also the crankpin from a needle roller? I hate making the interrupted cut on the lathe,

thanks
john

Yes, interrupted cuts can actually damage your lathe if you are not careful. What size lathe have you got? I thinmpfk that there isn't a person out there who actually "likes" interrupted cuts.

 

[xpylonracer]

Depending on what tooling you use, HSS or Insert type, you may achieve a better finish with heavier cuts, that applies especially to insert tooling, even the ground type intended for non-ferrous materials, perhaps a cutting fluid will help.

 

[Ramon]

Jetstuff

If you prefer to use it by all means use carbide tooling to rough your shaft to within 10-20 thou on diameter. Then switch to a freshly ground HSS knife tool with a slight radius for the final cuts.

EN24t will cut very nicely with a sharp tool but if the cutting point has even slightly worn it has the propensity to more burnish the material and remove nothing on the last couple of thou or so. The tendency then is to try another thou and still nothing comes off then perhaps another and suddenly the tool digs in and is under that 'skin' and the job is undersize.
I turn all my shafts to within 20 thou on diameter then regrind the tool for those last cuts to one to two thou up (max) polishing that last amount off with a fine file and or emery/wet and dry paper

Tug

 

[pat_pending]

Per John's original question above, I'm assuming a composite web and pin assembly wouldn't be possible as it would be too difficult fit and mount the pin with precise enough alignment? I used that approach on the Webster (silver soldered in) but the level of accuracy required on that engine is at the 'Garden Engineering' end of the scale vs these 14,000+ RPM aeros.

Patrick

 

[Ramon]

Patrick - Yes it is possible and several builders do use part of a needle roller for the crank pin - it is ideal material infact but it does, as you assume, have to be a very good interference fit and pressed in perfectly in line with the shaft. Not impossible nor exactly difficult but theres only one go at it. It's major limiting factor from my perspective is the limited thickness of the web relative to the diameter of the pin fitted. I've only done it the once and despite taking real care still was not convinced on the outcome.

I long ago was told before finally realising there are no shortcuts in enginering - just roads to further problems if taken.

Removing the waste around the crankpin in tough material and indeed the diameter of the shaft in the initial roughing are ops that just have to be accepted as a tedious part of the build and ones that take time on the basic home kit that most of us have at our disposal.

I much prefer to take small depth of cuts and a higher feed rate but whatever way it's not a job that can be 'pushed' or rushed. To my mind 'accept it as such' and it soon is out of the way ready for those final finishing ops.

Tug

 

[jetstuff]

Thanks again chaps. When turning between centres, what's the best procedure? The first shaft got hot, expanded and bent ! (with a locked live centre). It's a 7 x 65mm shaft with a M6 thread, on a Colchester bantam.

john

 

[Jasonb]

Sort out why it's getting that hot, your previous poor finishes may well be linked. Bigger jobs I would just unlock the tailstock barrel and take the pressure off and then reapply and lock every so often but something that small with little to come off should not be getting hot enough to cause problems.

On the subject of separate crankpins I have done 3 aero engines all with pressed in Silver steel (drill rod) pins and they ran OK for the odd few bench runs I've ever likely to do with them.

 

[jetstuff]

Sort out why it's getting that hot, your previous poor finishes may well be linked. Bigger jobs I would just unlock the tailstock barrel and take the pressure off and then reapply and lock every so often but something that small with little to come off should not be getting hot enough to cause problems.

It's getting hot because I'm machining a 20mm bar of EN24T down to 7mm without coolant

 

[xpylonracer]

Jetstuff

A way round the problem you found is to rough out oversize the length of shaft + a parting allowance with the EN24T 20mm diam stock mounted in the chuck, centre drill the end before parting off, fit the part to the chuck and face and centre the parted off end. Mount between centres to finish to size.

 

[pat_pending]

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:

http://modelenginenews.org/restored/conrods.html
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)

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.

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!

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

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

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.

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

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

Bye for now,

Patrick