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Member postings for Steve Crow

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

Thread: Smoothing a bore.
16/01/2022 16:46:03

A quick update.

I've had a go with Ramon's mandrel and wet & dry method and it works very well.

As expected, as the liners are a tight friction/force fit in the block, the bores had "shrunk" slightly when fitted. This was soon fixed.

I started with 800 grit and worked up to 2000. I did it on the watchmakers lathe under power at about 200-300 rpm. It does remove metal quite quickly like this (the paper loaded up in no time) but it is very controllable. I was able to get all 8 bores to have the same "feel" with the plug gauge.

I'm half way through making the pistons now.

Thank you to Ramon and everybody else for the help and suggestions.

Steve

Thread: Dovetail cutter and angles.
06/01/2022 22:32:22
Posted by JasonB on 06/01/2022 18:24:52:

Did you post that while I way saying the one with the cutter at an angle.

Another thread about them here

Yes, posts overlapped.

Useful thread, thanks.

06/01/2022 18:22:28

Maybe I should have explained a bit more.

What I am asking is which design of dovetail cutter would work best?

06/01/2022 17:54:57

I am looking to make a dovetail cutter using a 55 degree insert (DCMT?).

Would I be best using the insert "square" for a 55 degree dovetail like in the first drawing or leaving some clearance on the bottom for a 60 angle like in the second one?

dove1.jpg

Incidentally, the dovetails used on my Sherline machines are 55.5 degrees.

Cheers

Steve

Thread: Smoothing a bore.
03/01/2022 15:35:20

Thank you Ramon, I'm going to try your wet and dry method.

A couple of questions- How wide should the paper be in relation to the bore length and should there be some axial motion as well as radial when polishing? Also, would WD40 be a suitable medium (I have no paraffin)?

I've got to thinking about making hones for future projects though. Do you think this would work?

lap 1.jpg

The idea is that the lap is superglued to the d-bit and then drilled and tapped through both materials. The grub screw combined with the glue should secure the ali lap enough during operation. The screw is fine pitched for small adjustments.

Cheers

Steve

Edited By Steve Crow on 03/01/2022 15:44:21

03/01/2022 11:00:34

Thanks to you all for some very interesting suggestions.

Ramon, your lapping thread looks really informative, I will look closely at it now I have time.

I actually don't mind if the bores are increased slightly (I haven't made the pistons yet) as long as they are all consistently enlarged. I sort of took for granted that any polishing/smoothing/lapping would involve some sort of metal removal.

The reason for the go/no go gauges was to ensure that all 8 liners had a consistent starting ID.

If I go down the split lap route I assume that it will have to be made from something softer than brass, ie. ali?

I am liking the idea of Ramon's mandrel and wet and dry method. I don't mind a bit of low tech if it works!

I made a couple of liners with slightly under sized OD's which are now in the scrap tin. I suppose I could practice on these.

Thanks again and any other advice is welcome.

Steve

02/01/2022 16:50:45

I've just made the cylinder liners for my model V8.

They are bored out to 7.2mm and the OD is just over 8mm for a nice friction fit in the block. I made go-no go gauges to keep the bores consistent to 0.01mm.

liner1.jpg

I am not happy with the finish of the bores. I am looking for someway of smoothing/polishing them while maintaining the "roundness" and "parallelness" of the bores.

I am considering turning down a bar to a whisker under bore diameter, charging with an abrasive paste and polishing it that way.

Is that a good idea? And if so, what material for the polisher? A softer metal like ali. or harder like silver steel?

Also, would an axial or radial motion be the way to go?

I was thinking of Eucryl mixed with light oil (a toothpaste powder, I've used it before) followed by Autosol.

Any advice, suggestions or guidance would be much appreciated.

Cheers,

Steve

 

Edited By Steve Crow on 02/01/2022 16:54:16

Thread: My humble pinions
08/12/2021 18:11:26

Thanks Nigel, I did initially consider pre-parting them and I now wish I did for a few of them.

My problem is, apart from half a dozen gears, I don't know how thick I might want any other pinions to be.

I hate parting off gears. The teeth act like a musical box with a loud high pitched whine.

08/12/2021 16:55:30

Thanks Brian, I will be using some for a 1/12 scale V8 for the cam gear train and some more for a tumbler reverse gear in the matching gearbox.

Also I may use some for motion work in a clock project and to make a spur gear differential.

Steve

08/12/2021 16:18:24

I spent the weekend cutting gears.

There are 3X12, a 14, 15, 16, 18 and a 20 tooth, all Mod 0.3.

pin1.jpg

More sizes than I really need but setting up for pinion cutting is a bit of a pain so I thought I would "future proof" my parts box. You never know when you might feel a five-speed gearbox coming on.

Steve

Thread: Cosworth V8 1:12 scale
07/12/2021 22:58:48

My next challenge is to finish the cam gear train. The principal gears are in place and running smoothly, I just need to sort out the idler gears.

gears1.jpg

Here are some sat in their final position.

gears2.jpg

Steve

06/12/2021 15:10:28

One of the most fiddly things on this build was hand fettling the bearing blocks so the camshaft turns freely with a minimum of play.

cam1.jpg

The cam shafts are supported by a sort of shell bearing. These were made by turning down brass bar to 2mm and boring out to 1.6mm.

These were then trimmed down to a semi circular C-section and burnished/work-hardened into place using a polished steel 1.6mm rod.

They are now held firmly in place by there own springiness.

cam2.jpg

I'm making all this up as I go along but it seems to be working fine.

Steve

03/12/2021 17:27:22

Any chance of a photo with a rule in it so we can get a true sense of the small scale?

Dave

I usually put something in my photos for scale - I forgot this time.

To give you an idea, the total length of the assembled engine and gearbox is 85mm, 5mm longer than a cigarette.

Next time I take some photos, I'll include a coin or something.

Steve

03/12/2021 15:13:54

Hello,

I haven't updated this in ages so here are a few images of where I am with the engine and gearbox.

all1.jpg

all2.jpg

all3.jpg

I still have the pistons, valve springs and and a few minor things to make for the engine.

For the gearbox, I have to make the forward/reverse gears. I also need to design a clutch that will fit in here-

box1.jpg

The crossed-out side plates on the gearbox are tempory. I wanted to be able to see the diff but I've cut a "viewing window" in the top of the gearbox instead. The plates will be replaced with scale looking ones.

There is till a lot of work in finishing and polishing not to mention blueing about 130 screws.

More pictures soon.

Steve

Thread: Marking blue
29/11/2021 18:54:09
Posted by Dave Smith 14 on 29/11/2021 14:08:29:

Acetone or IPA.

Dave

Indian pale ale?

Thread: Help wanted with piston design
29/11/2021 18:50:11

After taking on board your advice, I have come up with this design -

piston2.jpg

Can anyone see any potential problems or means of improvement with this?

Also, I would be interested in any methods for introducing oil to the air supply.

In the intake manifold (plennum?) I have made, I've left space for bleeding off some air in case I need to inject some oil any where but mixing with the air supply sounds a lot simpler.

Cheers

Steve

28/11/2021 22:21:45

Thank you Jason, you answered pretty much all of my questions there!

I intend to introduce a bit of oil so I'll go for the aluminium.

Steve

28/11/2021 17:37:47

Hello, I'm 16 months into building a 1/12 scale V8, powered by compressed air/gas. The bore is 7.2mm and the stroke is 5mm. I will not be using rings. There is thread on here about it but I haven't updated it in ages.

I've made nearly all the parts but I haven't even started designing the pistons yet. I made the con rods and the crank nearly a year ago!

I haven't been able to find any help on the net as regards proportions of the pistons. I'm sure somebody here can help.

Here's a diagram to help me explain:-

piston1.jpg

My questions are-

Is there a rule of thumb for the proportion of D to x? I realise that having a bigger x will help keep the piston parallel.

Is it more advantageous to have the centre of the gudgeon pin (p) between a and b as in the first diagram or is it ok below as in the second?

Grooves as shown on the left. Are they a good thing?

Finally, materials. I haven't made the bore liners yet and have been thinking of using brass. For the pistons, I have no idea. I would like to keep the weight down, how about ali with a steel sleeve for bore contact?

Any ideas, advice or experience would be very welcome.

Cheers

Steve

Thread: Boring Head - Thread Quality
17/11/2021 17:32:57

Thank you Brian, I thought that they'd be rolled. Should be a better surface finish than cut as well.

I'm going to go for the commercial screw, even though it feels a bit like cheating.

M3 sounds really small but it is a tiny boring head, copied from this one but with an MT1 Sherline shank.

Cheers

Steve

17/11/2021 16:46:43

I'm making a small boring head with an M3 "leadscrew".

I can single-point cut the thread but I've considered using an M3 screw as I can retain the hex socket on the head for adjustment.

My question is, in practical terms, would give this measurably inferior results than a single cut thread?

I know this depends on the accuracy of leadscrew on the lathe doing the cutting.

On a side note, are commercial screw threads cut or rolled/formed?

Cheers

Steve

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