Member postings for Dave S

Evening all.

My no1 daughter has snapped the lug on her plastic watch, so I’m making a new case.

No it’s not cost effective, but why have a workshop eh?.

I was given a box of metal bars, including some stainless steel. One of the bars is a good size to make the case from, so I’ve had at it. It’s non magnetic, and it doesn’t seem to work harden or be the usual pig to machine that I’ve had in the past (316)

Is there any simple way to tell what alloy it is - so when I want some more I can actually buy it.

Dave

for simple 2D I use LibreCAD - it is much like AutoCAD but free, cross platform and generally quite useable.

Dave

Thanks all, sounds like a bit of a rethink is required.

If I come up with a cunning plan I’ll post it.

Dave

I want to cast some chess pieces. I have Pewter for the “white” as it’s east to melt and cast, but I’m stuck on a similar low temp, but not silver coloured metal for the “black” set.

Probably doing this with the kids, as they can make wooden moods for pewter.

Any metal suggestions?

Dave

My reading of the data sheet is that it’s a brushed motor servo with electronics to provide a step/direction interface.

there are also ones with a position input: **LINK**

If you search nema23 in the site they have a variety of rpm and interfaces.

I was thinking step direction would just “plug” into a grbl type controller without rewriting it.

Dave

Idly browsing around I have come across these:

**LINK**

Look like an ideal small cnc motor.
Anyone used them?

Dave

There is no need for a spring loaded tapping centre. The quill moves.

Bung a pointy or female centre in the chuck to guide the “free” end of the tap

for M4 you can turn the tap with one hand whilst pulling the quill down to support the back of the quill.

I regularly tap down to M1.6 using this technique.

For M5 and up (M4 if you are careful) a cordless drill makes a good tapping head.

Because it is doing the turning you can use both hands to make sure it’s guided square.

Dave

The facets come from the adjacent teeth on the cutter shaving the flanks / tops of adjacent teeth on the gear blank.

There is a bit of a thread here: Gear cutting with more pictures.

Yes the rolling will ultimately lead to the next tooth, but with a (say) 7 tooth cutter the roll can be completed from entry to exit of the “rack” at the target tooth. The adjacent teeth will also get shaved. Once rolled far enough then index to the next tooth and reset the Z to the start and do it again.

I planned to gear the roll to my TOS spindle somehow as that’s a fully manual machine, but I haven’t got round to it yet, and if I can get my baby cnc to work reliably the I was going to fix up a rotary axis and do it with cnc - but that’s a way off yet - the CNC nearly works, but so far it hasn’t really cut a complete part due to other distractions.

Dave

Yes. It's much like Hobbing in that respect.

All these were cut with the same cutter:

The pinions are profile shifted to avoid tooth undercutting.

There is potential to make 'better' than hobbed gears this way too.

If you don't roll the blank at all you get roughly 5 facets. With a hob you get a number of facets that is equal to the number of teeth on the hob. With coordinated Z and A you can get equivalent to the step resolution number of facets.

Dave

I was thinking of the cutter in the spindle, and rotating, more like this

Where the cutter traverses in x, and the blank rolls on the a (? Think that's x axis roll) axis synchronised with plunge in the z.

Spindle revs are then independent of the cutting of the tooth form.

Dave

I just respindled mine with a complete high speed spindle.

There are a couple of photos on the last page of this thread:

Link

https://www.model-engineer.co.uk/forums/postings.asp?th=166117&p=4

Dave

Edited By Dave S on 27/11/2020 19:22:34

Coming to this a bit late, but is the aim of the project to cut gears, or to make a hobber?

Bit of a left filed suggestion, but why not dispense with the threaded hob and make a rackform cutter.

With x,a and z axis you could cut whilst also 'rolling' the gear and simultaneously raising the z axis. Like a gear planer, but with a rotary cutter.

That is potentially doable by just plugging in a grbl to the 3 axis and figuring out the g code.

Dave

D R Mercer are also available from minsteam

Dave

Pretty sure American off roasters do something like this (air con pump as compressor).

IIRC they can then lower tyre pressures for certain sections of a trail with the ability to pump them back up as required.

Dave

For a 1 off at that size I would make a 60 degree point on a piece of silver steel, then file away the “top” to make a d bit. Add a little clearance on the none cutting bits. Harden and temper to straw.
To use you could hold in the tailstock and drill, or use like a boring bar in the toolpost.

for a larger cone then setting the cross slide over at 30 degrees (half angle) and feed in with that to bore - which is probably what is meant. The problem with that is the bottom of the bore - if required to be a point will need a boring tool which is very pointy.

Dave

If they are a cheap set then dismantle them and deburr the bits. A small dab of moly grease on reassembly helps as well.
“this old tony” on YouTube has a video on improving cheap bore gages.

Then using them is a question of practice mostly.
I do it like this:

select a gage where the range is appropriate - if there is an overlap I usually use the larger size gage as the telescoping pieces are less sticking out that way.
with the gage in springy mode plonk into the bore and cant over so the handle touches the side of the bore.
wiggle the gage a little so it’s as extended as it can be in the bore at an angle.

Then tighten the end piece so the gage will move, but is stiff. You may need to figure this out out of the bore until you have done it a few times.

move the handle from the side of the bore through the centre to the other side. Try to sweep in a single movement and along the diameter. As you pass through the centre the gage should tighten and then loosen. This is the bore squashing in the telescopes and then as you pass the centre they become shorter than the diagonal.

fully tighten the lock.

Only sweep once, then carefully remove the gage from the bore without bumping it.

Now you can measure over the ends gently. Be aware that a micrometer is also a g clamp - if you monkey it you will change the measurement.

You should be able to repeat measurement to under a thou without much practice, but it does take some practice.

If you have some ball races then you can practice with those, and know your measurements are correct, as the bores are quite tightly specified.

hope that helps

Dave

Does that mean you have a travelling steady for sale then?

Dave

On mine there are a pair of hole on the chuck side and a pair on the tail stock side:

I have no travelling steady, only the fixed one.

Dave

IIRC I run mine at 560, as it’s the closest speed on my mill...

Dave

When I had a pillar drill it was a cheap Chinese import - I think this particular one came from B&Q, but they are all quite similar.
I cured the quill slip by pulling the drill to pieces and then, after drilling a hole in the front casting about halfway up, slitting the casting. After bolting on a couple of bits of 1” angle to the sides I made a bolt with a handle so I could “squeeze” the slit.

Made the quill adjustable from “locked” to rattling fit - and so vastly improved the drill.

Then I got a proper sized Mill, with a huge quill and haven’t used a pillar drill since...

Dave