Member postings for Pete Rimmer

Be nice if you could try to use accepted terminology, and the correct terminology Brian. Some of your posts are quite chaotic in the poor choice of nomenclature.

I bought a 4-jaw for my HLV in very nice condition but it was a long time coming. The original Hardinge (made by pratt) 3-jaw is well past it's sell-by date.

If you're stepping out with calipers, marking, spotting then drilling the tolerance probably means that it's neither here nor there.

Compounding errors by stepping out isn't the best way to produce a gear anyway, dividing is much more reliable.

It would be a hob.

I would go with the above solution and helicoil the stripped holes. First though I would put a straight edge across the slide top and make sure it isn't bowed out slightly from whatever abuse caused the stripped threads.

Of course the tooth (not thread) form is different as the PCD changes. That's why we have numbered gear cutters, they are different shapes.

13TPI =0.077CP=40.8DP (41DP)

27.3/25.4=1.075" diameter blank

41x1.075=44.1 +2 = 46.1 so you should have indeed got 46 teeth on a 27.3mm blank the 28.07 diameter should have yielded 47.

Brian I only pointed out your error so that the uninformed don't become the mis-informed, please don't take it personally.

There isn't a simple solution because it's not a simple process. You don't find ready-made attachments for mill hobbing because the fundamental requirement for hobbing is that the work rotation be timed to the cutter rotation, and your average milling machine doesn't allow for that (there may be some ancient machines that take the table drive from the spindle drive by a geartrain and if you find one of them then you could possibly adjust the gearing to suit).

Your mention of the worm gear method bears some exploration. Unlike straight spur gears which can be cut with any diameter cutter or hob a worm gear needs to be cut with the same diameter cutter as the mating worm, or else the helix angle is wrong and tooth engagement departs rapidly from ideal. This is very prohibitive for the home engineer as buying custom cutters is very expensive so the most viable options are:

1. Make a hobbing cutter from hardenable steel that mimics the worm you will make with added clearance. Harden it and grind the cutter teeth sharp. Not a trivial exercise but doable though a lot of work for a single item.

2. Make a single-tooth cutter to the form and diameter of the worm, tilt it to the helix angle and cut each worm wheel tooth separately. A very laborious task.

3. Make or modify your design so that a stock thread can be used as the worm and then a stock thread cutting tap can be utilised as a cutter to hob the teeth onto a pre-gashed wheel.

No3 is often used out of necessity because it can give a good return of effort vs reward in terms of producing a workmanlike result for very little time and effort, The 'wrap-around' nature of the wormwheel teeth allows for a decent flank area for the worm 'cutter' to self-drive the wheel (unlike the spur gear's point contact) and if the material isn't too hard and the work well lubricated can produce very nice results. If the worm is pre-gashed (always recommended) you'll hit your desired tooth count every time.

The reason why pre-gashing is recommended for free-hobbing is because the pitch of the cutter (or tap, which is a hobbing cutter in this respect) is fixed but the pitch of the teeth on the wormwheel is larger at the OD than at the base circle and only matches the cutter pitch at the pitch diameter. When you start cutting the tips of the cutter will cut the edge of the blank and drive it somewhat however because the hob's pitch which is correct for the pitch diameter but starts cutting on the much larger OD it will naturally try to divide the OD into a greater number of divisions (teeth) than you require. Pre-gashing the work allows you to start your hobbing at a depth that matches the pitch of the cutter more closely to the pitch of the wormwheel at the pitch diameter which has two benefits:

1. You get the tooth count you want

2. The cutter will cut more equally both sides.

You see, by starting your cutting at the outside diameter the distance between each cutting start is 'short' for the tooth spacing at the OD, in order to continue towards full depth the cutter has to continuously shift the tooth profile around the blank away from the driving flank. When your cutting depth gets to the pitch diameter the pitch on the cutter is now correct for the cutting diameter and it will naturally cut the correct number of teeth. As you pass pitch diameter and approach full depth the pitch of the cutter is now 'long' for the diameter at the cutter tip which is why you get under-cut on small tooth count gears (not that you're going to get under-cut at 30 degrees pressure angle).

So, if you can gash the blank to at least the depth of the pitch diameter you stand a much better chance of getting a good result from your free-hobbing exercise in terms of correct tooth cound AND quality of cut because the load on the cutter and on the driving flank are greatly reduced.

So you see, worm-wheel fre-hobbing is borne of necessity but free-hobbing spur gears is not because there is no real requirement to. As you have demonstrated, it is actually possible but the result (subject to personal opinion) most often fall far short of what constitutes an even moderately well-made gear.

This is my personal take on the matter. Feel free to disseminate, disagree or criticise my thinking I will not be offended.

Pete.

Here's the page from the Herbert manual, if it's of any use.

Regards

Pete.

That ain't hobbing. Not sure what it is from this angle some kind of spiral gear setup but it's using a form cutter to cut the tooth directly not a hob to generate the involute.

My Herbert 0V milling machine has a page in the manual for doing this very thing (actually for copying dies, but it's the same principle). It describes using a ball-ended cutter and an identical probe (just a metal rod with a round end the same diameter as the cutter) set over the pattern. It has a fast-travel x-axis screw too (2.5tpi) to facilitate the work. The cutter and probe are set up over their respective parts, the operator keeps weight on the quill handle and uses the traverse to run the proble over the die to be copied. The cutter follows the path of the probe and makes an identical pocket needing only minor finishing.

A bit like a lathe hydraulic copying attachment except fully manual and producing 3-dimensional copies rather than the lathe's 2-D.

This can happen with a proper hobber too. Mine is often noisier when starting off a pass but quietens right down as the cutter engagement increases.

The large barrel micrometer heads are tenth-reading micrometers. Mine came off a measuring stage.

I fitted a small single phase motor to drive the pump on mine. Wkred perfectly fine. I also ran the main motor from a VFD but since it was a very early model with only star winding I had to get the motor apart and split the star point so I could re-wire it for delta. This too was perfectly sucessful.

I had a 'day out' some years ago having a go in several older-model flight simulators along with a couple of other guys. We were all aquainted with one of the operators and it was a rare day when there were no machines booked.

It was a great fun day. I managed to land a 737 on finals at Gatwick, albeit running off the end of the runway but apparently it did qualify as a succesful landing.

I also managed to land a Sikorski, unfortunately tail-first :D

I could see their value as a training aid. The noise, vibration and movement makes your brain fill in the blanks to convince you that you really are flying the plane. Well, almost...

Your will fell off? Hope you weren't going fast at the time

https://www.thingiverse.com/thing:4043256

Drawn with Sketchup.

Nick a van cannot be classified as a car-derived van if it's laden weight is above 2 tonnes.

I saw one a couple of weeks ago. i just exited the Dartford Tunnel heading North when the car in front suddenly swerved to the left, and I was forced to do the same due to a mountain bike laying across the line between the lanes. About half a mile further on there was a car on the hard shoulder with a pair of bicycles on his 3-bike roof rack and a space where the third should be.

Hi Beccy.

The big chuck at the far right end does not belong on that machine it's for a muc larger lathe, also the tailstock (the thing it#s hanging on is fitted backwards. The pointy end attachment should point at the chuck on the left.

Your dad's lathe appears to be largely complete although the sapearate wall-mounted countershaft makes it a bit cumbersome. In the cabinet the only parts that belong to it are the gears and the big round faceplate with the slots. Loks like there is a tilstock chuck too (it fits in place of the pointy end dead centre in the tailstock). The grinder wheels and other bits are not meant for a lathe (although he may well have used them in it). The wooden thing in the corner is a hand tool called a wood plane.