Scratch build Nitro tethered race car, second try!

[Roog]

I was gifted a beaten up Irvine .20 glow engine so I am planning to build a nitro powered tethered race car based on the classic 50’s style with a Grand Prix body from that era. It is intended that the car will have an RC throttle!

My first issue is that the engine came fitted with a centrifugal clutch which isn’t helpful because tethered cars are generally push started. So I need to make a new flywheel which can interface the pinion gear from a set of matching bevel gears.

The engine drive shaft is short so I have had to figure out how to fix the pinion gear on securely.

My biggest fear is making the split tapered collet and matching internal taper in the back of the flywheel. I’ve not had much luck grinding miniature boring bars to fit inside a 1/4” hole. But a friend on the UK model engineering forums suggested buying a ready made tool from Ali express, I was sceptical but it seems to have worked a treat. The first issue was it’s really small 4mm shank and I had to make a collet to hold it in the lathe tool post.

It’s only a little tool but it was quite rigid.

So here’s the first part built

Complete with pinion gear located in deep recess in flywheel. The flywheel will have a couple of drive pins set inside the recess to engage with a slot in the rear of the pinion. To get around the issue of the short drive shaft my friends from the UK tethered car club suggested I make a sleeve nut, (I had to look that up), so once I’ve had a go at making the split tapered collet to match the internal taper in the rear of the flywheel, the sleeve nut will be next on the list.

Just in case there is any confusion I bought the bevel gears, they are spares to fit a Hitachi angle grinder.

The plan is to make a sturdy sub chassis mounting the engine, the rear axle and locating the bevel gears which will be doing their best to push each other apart!

I’ll then consider how to attach the chassis rails and consider whether I want to pivot the subframe to introduce basic suspension.

 

[Beer_Goggles_RC]

Dude this is crazy impressive. Are you a machinist by trade?

 

[Roog]

Thank you @Beer_Goggles_RC , I am a keen amateur having tinkered as a teenager using a really tiny lathe, a Unimat 3, and 4 months at an apprentice training centre which was just a taster for what the company did, they sent all of their under grad engineers to get the experience, but it did allow me to play with half decent machines and to get access to a bit of proper training.

I am an electrical / electronics engineer by training, I just like making things and when the opportunity arose to pick up a small and well used lathe locally I jumped at the chance to get back into it after a 40 year gap.

I find it fun but frustrating, as the machine is limited and I am making it up as I go!

Others, here on ‘RC Talk’ do know what they are doing with machine tools and they have been really helpful in my last project, ‘Scratch built electric tethered race car’. With any luck they will help me out again.

 

[WickedFog]

So it begins again

 

[Roog]

@WickedFog Ha ha, yes it does, I have to do these things to stay sane (actually that’s debatable)

Next step is the split tapered collet to match that of the flywheel.

Having kept the compound slide at the taper angle the plan is to cut the collet at the same angle.

A quick try by pushing the flywheel on and success, it fits!

Having parted ‘cut’ the piece off in the lathe, I flipped the now very small and awkward piece around and push fitted it in the flywheel and faced off to the final depth.

Next I removed the collet stuck it in my vice and cut the slot by eye using a jr. hacksaw, I should have used a slitting saw in my mill, but I don’t have the blade.

Final part

Next up is the ‘clever’ bit the sleeve nut, this allows me to fix the flywheel plus pinion gear on to the engine shaft even though the shaft is not quite long enough.

I’ve put some 1/2” hexagon bar in the chuck centre drilled it and drilled to tap size for the internal thread size of 1/4”-28 UNF which I believe is the thread on the end of the engine shaft, fingers crossed. I turned the part down to 10mm to fit the gear I/d lapping it to size with fine wet and dry paper. I then tapped the hole by putting the tap in the tail stock of the lathe and turning the main chuck by hand back and forth. It’s hard work but it is important that this part is concentric.

It’s a good idea to turn the lathe off at the wall isolator, because it is easy/instinctive to start the thing once you have set up. This would be very bad with a fine tap in the bore!

 

[Roog]

One thing, when tapping blind holes, how come the plug tap/no. 3 tap, (the last one) has a fair o’l point on it? This stops the tap getting to the bottom of the drilled hole? I ground it off, shock horror. For reference the tap hole size was 7/32” it might not be funny on your side of the pond but it’s quite unusual for me to have to dig out my imperial drill set these days :0)

Here I am parting the sleeve nut off

And it falling off

And the final part

And to my utter amazement it all fitted together. What I didn’t show was drilling and tapping the two M3 drive studs inside the flywheel which engage in a slot cut into the back of the gear.

Next up is to make the sub chassis to mount the engine and rear axle. I’m going to use 22mm diameter ball races set into aluminium side cheeks.

I’ve not finalised this up yet as everything I’ve drawn so far looks hard work and a bit chunky, plus I need to figure out how to bore the 22mm holes. Up to now I have got away with small holes and using flat bottomed drills but at 22mm that’s a big ask for my little mill.

Ideas welcomed, I gather a boring bar might be the way to go, but I don’t own one, yet.

 

[Roog]

Moving on to the engine gear box sub frame, I need to make some accurate big holes in which to mount the rear axle bearings. After an exchange of views on the model engineering forum I bought a boring attachment for my mill. First set up material in the vice, face off ends to length and touch off each face to find the centre from one end, moving the piece 50mm in from one end we now have the centre from which to make the 22mm hole.

Drilled out to 16mm with a combination of twist drills and 2 flute end mill/ drill I tried out the boring attachment for the first time.

The tool is very much like a lathe tool but the tool spins in the head and can be made to make smaller holes bigger from the inside or large circular things from the outside.

The way it works is a bit tedious, set tool position, make cut withdrawal tool, measure resulting hole, adjust tool and on and on until you approach the final diameter.

The tool is moved by a screw on the side of the head which progressively moves the tool away from or closer to the mills axis of rotation, and can only be adjusted with the head stationary.

The final size within reach on the second piece, I have also drilled the holes for the bearing retaining screws

Slow and steady is the only way.

After a bit of milling to remove material where the chassis rails are to emerge, I haven’t posted the drawing of the chassis yet, but the plan is to make it as an old fashioned ladder using C-section rails.

I have two side cheeks ready to take their bearings. Not messing around this time it’s ball races front and back.

For such simple parts that took a long time to do.
Moving onto the engine mounting plate and spaces next.
And I’ll see if it worth drilling 16mm holes in the side cheeks to reduce weight a little, they do look a bit clumpy!

 

[CertifiedMike]

I'm loving this build! If you're an amatuer now, I can't wait to see your pro builds!

 

[Roog]

Thank you Mike, it would take a fairly big change of mindset for me to do a pro job, I get bored too easily, but my efforts are usually close enough

Looking at the last photo I am getting worried that this model is going to be a bit heavy, again!

 

[Roog]

Moved on to engine mounting and crown gear hub today

Here I have cut a length of U-channel and in am milling the edge to length and square.

Bit dodgy really but if you take small cuts and take some time it stayed put whilst machining.

Next is to cut the slot for the engine by roughing out the cut with a hack saw then stitch drilling the dead end

 

[CertifiedMike]

Ok so... maybe I'm goun- to start WWWIV here BUT... I have SOME limited machine experience.
Due to the nature of soft, white metal aluminum, its break strength comes from its surface tensile strength. What this means, if I understood this correctly. Is that with strategic material removal, you will lighten the part AND gain strength.
There are ppl here FAR more capable at explaining why this may or may not still hold true some 30+ years later.
Your build is really cool! I'd love to see a finished run!!!

 

[Roog]

To fit the crown gear I need a nub, the crown gear has a 14mm dia. hole for the shaft, but the shaft is going to be 10mm dia. The hub also allows for some alignment across the chassis left to right.

Having got the mild steel bar down to 14mm to fit the gear, I have to drill then ream the internal diameter to 10mm.

After test fitting the gear, I parted the piece off and flipped it around to machine the other side to length.

Here I am drilling from the other side, this gives slightly better centring as drills tend to drift over deep holes so doing half and half from each end gives the best results. The hole was then reamed to final diameter 10mm.

 

[CertifiedMike]

To fit the crown gear I need a nub, the crown gear has a 14mm dia. hole for the shaft, but the shaft is going to be 10mm dia. The hub also allows for some alignment across the chassis left to right.

View attachment 205374

Having got the mild steel bar down to 14mm to fit the gear, I have to drill then ream the internal diameter to 10mm.

View attachment 205375

Again, SUPER impressed!!!

 

[Roog]

Here is the final hub part with crown gear which had to wriggled on. It needs to be removed so that I can cut a key way.

I have made it over sized in length, this can be ‘trimmed’ in the final fit.

And here are the main parts laid in their rough positions so that hopefully you can make sense of my work so far.

The bad news is that for the last few ‘drilling’ operations the lathe start wouldn’t latch in, but it would start, so I held the start button in! I tried each of the safety switches and they seem to work as expected so it’s likely to be something in the controls section.

I have had all of the covers which cover electrical bits off and my biggest worry is that there is an issue with the main control board, however eventually I found the fail safe latching relay/contactor, and I noticed that the usual click isn’t happening any more, I am hoping that it either a cable that’s fallen off or that the relay has burnt out. First rule of troubleshooting look for the simple stuff first.

Must check fuses too!

Here is the combination start /stop latching relay unit. I know that pin 14 goes live because the motor starts if you hold the button in, but I’m not sure what is connected to pin A1, yet, that’s a job for a spare moment over the next couple of days in between bursts of actual fee paying work like stuff!

 

[332_RC]

Awesome machine work! Machinist here

 

[Roog]

Ok so... maybe I'm goun- to start WWWIV here BUT... I have SOME limited machine experience.
Due to the nature of soft, white metal aluminum, its break strength comes from its surface tensile strength. What this means, if I understood this correctly. Is that with strategic material removal, you will lighten the part AND gain strength.
There are ppl here FAR more capable at explaining why this may or may not still hold true some 30+ years later.
Your build is really cool! I'd love to see a finished run!!!

My last car was really too heavy, so i am going to make more effort this time, less is more!

I will try to get some video footage when the time comes. I am going to try a couple of novel ideas out on this car, the idea is to make IC tethered cars less reliant on specialist parts. I just hope they work, if my last efforts are anything to go by exploding tires is my specialty :0)

Awesome machine work! Machinist here

I’m glad one of us can do it properly!

Honesty, this is for the fun of making things, just like RC but with the added dimension of starting with plain lumps of metal, you get to make stuff from your imagination.

It beats making steam engines or as my missus is happy to tell me, expensive paperweights.

 

[CertifiedMike]

My last car was really too heavy, so i am going to make more effort this time, less is more!

I will try to get some video footage when the time comes. I am going to try a couple of novel ideas out on this car, the idea is to make IC tethered cars less reliant on specialist parts. I just hope they work, if my last efforts are anything to go by exploding tires is my specialty :0)



I’m glad one of us can do it properly!

Honesty, this is for the fun of making things, just like RC but with the added dimension of starting with plain lumps of metal, you get to make stuff from your imagination.

It beats making steam engines or as my missus is happy to tell me, expensive paperweights.

I've got an EXTENSIVE collection of "home-made ashtrays" that I might be willing to trade for a tasty vintage Kyosho...
Just sayin...

 

[Roog]

Replacement switch unit has been ordered and hopefully normal service will be resumed soon.

 

[Roog]

Lathe stop start switch replaced and it turns!

Today I had a session drilling holes to assemble the rear sub frame parts

And after shaving a bit off the end of the crown gear hub I put the bits together

Not that it’s obvious from the picture, but to test my lathe I chose to reduce the diameter of the engine flywheel by 5mm in a vain hope to reduce weight.

 

[Roog]

Today I had a go at cutting a slot in the drive shaft for a key, I am not sure if it is strictly correct but I know them as a woodruff key?

2.5mm diameter end mill cutting a slot 2.2mm deep, 3mm wide and 8mm long. The shaft is 10mm ground silver steel, it’s not super hard but I had to take it easy with such a fine tool.

Next up is crown gear hub, because the key has to pass through the hub as well I need to cut the same slot in the correct place.

Being of mild steel this is easier to machine.

Here they are together, they line up!

Next is the key, 8mm long, 3mm wide and 6.3mm deep, I forgot to photograph making the key, I milled one side off, flipped it 180 deg then machined the same depth off the other side to create an oval, here I am parting off in the lathe.

At this point I assembled the parts with the gear and realised that the slot in the crown gear was actually 4mm wide (should have measured not assumed), so I ended up re-machining the parts again to make the slots wider and make a new key to fit, despite doing it much quicker the second time around it turned out well being a tighter fit.

For a first time effort I am quite pleased with the result.

I just hope I’ve put the slot in the shaft in the correct place, because it fixes the position of the shaft across the width of the car.