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1  General Category / Gear Discussions / Re: Profile for Screw Compressor? on: April 28, 2016, 06:58:01 AM
I have collected a few theory papers for the screw shape off the web.
The maths for the screw shapes is ... a bit intimidat ing. Yes, I could program the curve, but HEAVY! Roots are much simpler, but limited for pressure.

Hum - moving on to scroll compresso rs ... the maths is simpler.

Cheers
Roger
Edited to clear up the confusion - sorry Nate.

2  General Category / Gear Discussions / Re: Profile for Screw Compressor? on: April 28, 2016, 06:29:08 AM
According to Wikipedia, the problem with Roots Blowers (for my needs) is that they are more high volume /low pressure. I need 5 or 6 bar, and I don't think a Roots can do that? But I don't know.

Cheers
Roger
3  General Category / Gear Discussions / Re: Profile for Screw Compressor? on: April 28, 2016, 06:16:07 AM
A Roots Blower ...
Now there's an idea! Much simpler. But do you have the equations for the impellors?
I wonder how noisy the sync gears would be at full RPM?

Cheers
Roger


4  General Category / CNC Machine mechanical questions / Re: Mach3 Pendant Question on: April 28, 2016, 06:10:10 AM
I have the same unit.
I THINK if you jiggle the Shift key 7 times Windows will ask you if you want it to be 'sticky'. This is fo people with disabilit ies. This might work.

Cheers
Roger
5  General Category / Gear Discussions / Profile for Screw Compressor? on: April 28, 2016, 06:05:24 AM
My piston compresso r is very noisy, and has to run a lot when I am machining with air blast and pulsed mist. I want a quiet compresso r - but with adequate pressure and flow.

A screw compresso r would be nice, but they tend to be larger than a big piston compresso r, and they also tend to be $$$$. Their advantage is that they are much quieter.

Could I make some small screws on a CNC with a 4th axis? If I had the profile I am sure I could have a go. But typically the screw has only 3 or 4 flutes, and the profile is going to be ... odd. There has to be full engagemen t  to lock the air in of course. Has anyone any ideas? (Is this a gear? Dunno ...)

Cheers
Roger
6  General Category / Gear Discussions / Re: Miniature Taper Lock fittings? on: April 28, 2016, 05:58:15 AM
In the end, I found that a 2011 aluminium taper inside a 2011 or 6061 aluminium pulley on a steel shaft did not need a key of any sort. Once the taper has been done up tightly, you need a hammer to break it loose. All very successfu l.

I will have to make a good gear-puller to get them back off the shafts ...

Cheers
Roger
7  General Category / Gear Discussions / Re: Cutting Timing Pulley Teeth on a Lathe on: April 28, 2016, 05:50:27 AM
SDP-SI have an excellent screed on tooth belt dimension s.
For GT2 the rules are as follows:
A toothed pulley with N teeth has a pitch circle diameter (PD) of 2.00*N. (The pitch on the belts is 2.00 mm)
The radial distance between the PD circle and the Outside Diameter (OD) circle of the pulley is 0.010" or 0.254 mm, by definitio n. (So the differenc e in diameters is 0.508 mm.)

The actual GT2 profile is in the Gates patent, but they have managed to draw the diagram in a reasonabl y incompreh ensible form. This is of course entirely accidenta l ...  Wink

If you search through the SDP-SI web site you will find that you can download a DXF for any of their stock pulleys. Fine - but with a tiny bit of knowledge you can open that DXF up to see what the profile looks like, in terms of arcs etc. How nice! However, be aware that the DXF drawings are NOT an exact represent ation of the Gates profile. The DXF is several microns wrong in several places.

If you search through the web you will find Chinese GT2 belts and pulleys. Well, they CALL them GT2, but they are not licensed by Gates afaik, and their profiles are a bit more off. You may also find their idea of the profile as well.

Other good brands have profiles which are very similar to the GT2, but they have to call them something else because of the patents etc which Gates holds.

Now, some backgroun d to explain all this. The GT2 profile is very similar to the HTD profile, but the HTD patent expired. So Gates developed and patented the GT2 almost entirely as a successor to the HTD, rather than for any really serious technical reason. The GT2 patent has now also expired - so Gates now have the GT3 patent ...  Fortunate ly, even Gates admit the GT2 and GT3 are compatibl e. In short, the differenc es are small.

The big advance is the curved profile on the belt which snugs into the pulley, as opposed to the loose and rattly profile of the old XL-type belts. Since the rounded teeth engage so much better, the rounded tooth belts are both quieter and transmit more power. And the GT-style has almost zero backlash, which is a lot better than the XL ever were.

I have been cutting GT2 pulleys in various sizes, with good success, to upgrade my CNC. They replace the old XL belts it came with.

Cheers
Roger
8  General Category / Gear Discussions / Re: Miniature Taper Lock fittings? on: March 18, 2016, 08:09:21 PM
I tried putting a keyway into the taperlock, but that meant drilling or broaching a 1 - 1.5 mm hole down the boundary between taperlock and pulley at the taper angle for maybe 10 mm. That was ... difficult .

The single nut works very well imho.

Yeah, I understan d about your more 'senior' members.  Smiley Given the hassles of maintaini ng a CNC, I don't blame them.

Cheers
Roger
9  General Category / Gear Discussions / Re: Miniature Taper Lock fittings? on: March 18, 2016, 06:49:15 PM
Zip file received. Interesti ng article (and issue), for which my thanks.

Ah, model engine enthusias ts, and the smell of nitro ... (or ether+olive oil)

However, about half the article has to be devoted to explainin g how to get +4.0 degree and -4.0 degree tapers on a manual lathe, with the admission that the 4 degrees will still only be approxima te. This is fine if one is restricte d to a manual lathe, but I suspect that most readers here will be running CNC machines. With a decent CNC lathe you just specify 4.00 degrees in the code and that is it. An extremely accurate match results. (Yes, I do have a manual lathe and a manual mill as well.)

I did have some reservati ons about scale. Your taperlock design uses 4 - 6 bolts to tighten the taperlock into the pulley. Some of the taperlock fittings I am making, or rather the pulleys they are being fitted to, would require 1 mm bolts for that to fit into the space provided. A shade too small I think. Instead I went for a single nut over the whole taperlock . That is just a detail: on a larger taperlock the flange+bolts would be better.

Cheers and thanks
Roger
10  General Category / Gear Discussions / Re: Miniature Taper Lock fittings? on: March 18, 2016, 04:26:49 PM
Quote
Not wanting to blow my own horn but I published an article on how to make taper lock bushings in issue # 11 of Model Engine Builder magazine. This type of mount for flywheels is frequentl y used (and made) by Model Engineers .
So many magazines, so little time. Thank you.

Quote
Tapers are always a bit tricky to cut because not only do the tapers, male and female, have to match, they must be cut directly on center or they will not have straight sides.[/quote
And trying to match the tapers on a manual lathe is a right pain. But with a CNC it is easy enough.
'On centre' - yes, a hidden trap. But it can be handled.

I have PM'ed you.

Cheers
Roger
11  General Category / Gear Discussions / Re: Miniature Taper Lock fittings? on: March 17, 2016, 08:01:30 PM
Photo as promised below. From top downwards:

Two large pulley blanks, one in PE and one in 6061. I KNOW the PE is not as strong as the 6061, but the diameter is 3x that of the smaller 6061 pulley, and I know the teeth on that size are strong enough. I know that nylon, in quite thin sections, is often used for toothed belt pulleys. So - an experimen t. I suspect the teeth on the PE pulley will turn out excellent .
The PE blank has a taperlock unit in it, with brass nut. The big Q is whether the taperlock will hold against the PE, or whether it might slip. I don't know yet. I don't think cracking is a worry with industria l PE this thick. If it does slip I can put an Al bush insert into the PE with flange screws: commercia l nylon pulleys have Al bushes and the nylon is molded around the bush.

Test GT2 pulley, 30T. Just one of a number of GT2 pulleys I have made. The others are actually in use. My cutter (which I made) may deviate from the official GT2 profile by a micron or two, but should I worry about a few microns when the belt face is fabric?

2011 Al alloy pulley in middle. There will be a 3:1 ratio between the big and small pulleys when they are finished. Yes, the bore in these blanks is tapered already: 3 degrees half angle.

TL insert on mandrel. It has 8.00 and 9.50 mm ends.
Taperlock inserts for 8.0 and 9.5 mm shafts: you can see the slightly different wall thickness es.
TL inserts showing anti-rotation key slots used only when tightenin g the fitting
Pulley showing pin going through plulley into TL insert. (In this unit the key slot overlays the split, which has been hacked around a bit during experimen ts.)

Still to do: turn the ODs of the blanks down to correct values; cut GT2 teeth onto blanks; make up side flanges and fit to pulleys; fit and test.

Cheers
Roger
12  General Category / Gear Discussions / Re: Miniature Taper Lock fittings? on: March 17, 2016, 04:25:59 PM
Quote
It looks like Ringfeder does make a 7090 taper lock in that size.
Indeed. I have enquired about pricing. I await the reply with great interest (and doubt).

Cheers
Roger
13  General Category / Gear Discussions / Re: Miniature Taper Lock fittings? on: March 17, 2016, 02:15:58 AM
Quote
Is it possible that it's a 3/8 inch part (about 9.53 mm) and the 8mm shafts are 5/16 inch (about 7.94 mm)?
What a horrible thought!
It was built by an Australia n company, and Australia went metric in the 60s, but it may be that the company was still using imperial in some places where they were dependent on American parts - such as ball screws and toothed belts.

Hum ... It's possible. I will have to find out when I take the XL pulleys off and put the GT2 ones on. Fortunate ly, since I am using split taperlock fittings, there is some room for a few 10s of microns variation .

Thanks for the suggestio n anyhow.
Cheers
Roger

14  General Category / Gear Discussions / Re: Miniature Taper Lock fittings? on: March 16, 2016, 10:50:39 PM
Ringfeder - yes, they have small taperlock s. 8 mm, 9 mm, 10 mm, but not 9.5 mm.
Do not ask me WHY the mfr of my machine chose 9.5 mm - I don't know!

In essence, what I am making is very similar to a Ringfeder RfN 7085, but with the outer taper as part of the pulley itself. Well, I have to bore the hole in the pulley anyhow: why not bore it as a taper?

Cheers
Roger
15  General Category / Gear Discussions / Re: Miniature Taper Lock fittings? on: March 16, 2016, 09:18:40 PM
Hi John

Ah yes, Small Parts - our favourite gold-plated unafforda ble supermark et. Sorry, but their local (AU) pricing puts them out of most hobbyist's reach. OK if on a Defence contract maybe.

That coupling on p303 might be OK for some light duty work, but it would NOT suffice on the drive for a CNC axis. We need far more security than that. There has to be zero risk of slip or backlash.

However, you mentioned other sources for miniature Taper Lock fittings: please, details!

Cheers
Roger
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