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Thread: Mars Mercury lathe
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13th Jul 2020, 04:54 PM #16Most Valued Member
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At a guess taking wear into account they are probably 14 DP.
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13th Jul 2020, 05:46 PM #17Gear expert in training
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Sorry, I did see but thought I'd check if we had a hob first.
You're both correct, 14DP 14.5° PA
Unfortunately we only have a 14DP 20° hob, our 14.5° range tops out at 15DP; the other half of the company that deals with larger gears has one in 14.5°, but it's much too big to fit our machines. They will be able to make them for you, but it will be at the normal shop rate, not the "after hours private job special"
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14th Jul 2020, 01:52 PM #18Novice
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[QUOTE=elanjacobs;1971411]Sorry, I did see but thought I'd check if we had a hob first.
You're both correct, 14DP 14.5° PA
Unfortunately we only have a 14DP 20° hob, our 14.5° range tops out at 15DP; the other half of the company that deals with larger gears has one in 14.5°, but it's much too big to fit our machines. They will be able to make them for you, but it will be at the normal shop rate, not the "after hours private job special"[/QUOTE
Hi elenjacobs,
Many thanks for your efforts and reply. This may be sacrilegious to a gear make, but what would be the consequences in this application of meshing 14.5 and 20 degree pressure angle gears of the same pitch together? I have attached a marked up scanned photograph of the arrangement which shows gear no.1 and gear no.2 from my previous post are permanent fixtures and mesh with a 20 tooth idler tumbler gear which of course would be worn.
From the stub shaft of gear no.2 to the lead screw various gears are arranged in accordance with the thread cutting guide chart to accommodate different threads per inch. I guess if the worst came to the worst, a new 20 tooth idler gear with 20 degree p.a. could be made?
What do you think?
Regards,
Rob
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14th Jul 2020, 02:28 PM #19Most Valued Member
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You could completely convert to 20 degree pressure angle.
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14th Jul 2020, 06:29 PM #20Gear expert in training
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If those 3 gears don't have to mesh with anything else, converting to 20* would be the way to go. Mixing pressure angles is....not good; they feel "notchy" when rolled together and will run louder and wear much faster. It also requires extra clearance, so if the centres are all fixed the gears would need to be cut with a correction factor to allow (above my pay grade for the moment).
It's like a space-saver spare wheel; it'll get you out of a bind if you have to, but don't go too fast and put the proper one back on ASAP.
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14th Jul 2020, 07:57 PM #21Novice
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Hi elanjacobs,
Again many thanks for your help and advice. I now realise that I need the second 20 tooth tumbler gear to be able to reverse the direction of rotation of the gear train. I found a badly stripped one in amongst all the bits and pieces that came with the lathe.
So in summary, if I stick to the 14.5 degree pressure angle I will now need three gears cut. You mentioned in an earlier post another branch of your firm which could cut the 14.5 degree gears. Would it be possible for you to get a quote to make the three gears if I send details of the additional 20 tooth tumbler gear tomorrow? I believe the original gears are cast iron, but replacements should be steel. Will leave the choice of grade up to you. Many thanks,
robjean
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14th Jul 2020, 08:26 PM #22Philomath in training
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There are several firms around the place that cut gears, but it will cost you $100's. Several of us cut gears and may be able to cut them for you if needed.
Michael
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14th Jul 2020, 08:33 PM #23Gear expert in training
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Best if you contact them directly instead of back and forth through me https://www.hardmanbros.com.au/contact
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14th Jul 2020, 08:37 PM #24Diamond Member
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On US based machining fora Boston Gear is often mentioned as an answer to someone's broken/missing change gear problem.
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14th Jul 2020, 08:47 PM #25Most Valued Member
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Ronson gear in Melbourne also carry a good range of stock gears made by KHK who's catalog is publicly available. Prices are pretty good.
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14th Jul 2020, 08:51 PM #26Gear expert in training
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I had a look at the KHK site via Ronson at the beginning and they don't seem to have 14DP (unless I missed it); apparently it's a bit of an oddball size, it usually jumps from 12 to 16 DP
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14th Jul 2020, 09:25 PM #27Pink 10EE owner
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Ahh you work for them. Here is one of their gears.
I hit a few too many rocks in the slasher. It still goes round and round.
20200613_171510.jpg
As for the lathe change gears. I would make them out of cast iron. Easier to machine then steel. Someone with a CNC mill with a CNC dividing head and gearotic could do it pretty easily, even a metric transposing gear.
There is always a gear cutting set. https://www.ebay.com.au/itm/8-Pcs-In...8/293622567298Gold, the colour of choice for the discerning person.
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14th Jul 2020, 09:42 PM #28Gear expert in training
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I work for R&I, Hardman's bought us a while back, but it's all in the same place. They do the big stuff, we do the (really) small stuff; we have hobs going all the way down to 0.1 Mod
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14th Jul 2020, 10:41 PM #29Gear expert in training
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15th Jul 2020, 03:48 PM #30Most Valued Member
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I have also had gear cutting and manufacturing in seaford hob me 14DP gears before at reasonable cost.
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