Model Engine Maker
Help! => Specific Engine Help => Topic started by: Kim on January 05, 2014, 06:27:48 AM
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Or grub screw, if you prefer :)
In my current build, the plans specify two set screws in the fly wheel - 180 degrees opposed. See the plan excerpt below:
(http://lister-engine.com/coppermine/albums/userpics/10008/028a-FlyWheel-FlyWheelSetScrew.jpg)
However, I've heard that you should never place set screws directly opposite of each other, because then you're suspending the flywheel on the two set screws and not getting all the additional surface area of the shaft making contact with the wheel.
Would you ever want to use two set screws? And would you use them opposing as showed? or at some other angle?
Is there ever a reason to have more than one?
Thanks!
Kim
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On the hub on the front of my crankshaft I put 2 screws in. The hub is what the starter spins so it takes some abuse. I put 2 screws at 90 degrees apart that mate with 2 flat surfaces on the crankshaft. Haven't had any trouble sence.
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You have heard right Kim - always use 'em at 90° or thereabouts - never at 180°.
In most cases a single grub screw is enough, but just occasionally you might have install a second one. There is a good case for that with valve eccentrics where, once set properly you can remove one, dimple the shaft, reinstall and ditto repeato for the second one.
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Highly stressed parts will often have two grub screws down the same hole, the second one in locking the first like lock nuts. Often confuses people on dismantling . . . 'why can't I pull it off, I've removed the grub screw ' ... :thinking:
Andrew
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:D Yes, I've been caught by that more than once!
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On the agricultural machinery that I'v been involved with, we make our own chain sprockets etc., they are on 35 mm shafts, with 10 mm keys, our method is; one grub screw on top of the key, the other 90* from that, we use 3/8 UNC x 3/8", seems to hold OK, the shafts sometimes get bent, or broken, don't think we'v ever had problems with the keyed fittings.
Fitted a pulley on a 3hp Kawasaki motor yesterday, noticed that it had one 5/16"grub screw opposite the key, everything is nice and tight, so it's staying that way. Ian S C
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Most small engine designs like this are shown with the grubscrews opposing, it is probably done in the belief that it will balance things out. As has been stated earlier the grubscrews are more effective at 90 degrees, and if the shaft has two flats at 90 degrees also this is a very effective means of locking the parts together.
If the two grubscrews were equally displaced 45 degrees either side of top dead centre then the flywheel will add to balance the engine, especially if the there is a disc crank.
My best regards
Gray,
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Highly stressed parts will often have two grub screws down the same hole, the second one in locking the first like lock nuts. Often confuses people on dismantling . . . 'why can't I pull it off, I've removed the grub screw ' ... :thinking:
Andrew
I did the same thing on the V8. Took both 3/8 long screws out and put 4, 3/6 long screws in. 2 down each hole.
I had a problem with the hub coming loose in the middle of the day at Maker Faire Detroit and I wanted to make sure that never happened again. Might be over kill.
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Two screws placed at 90 with jam screws behind them is best practice, however,,,,I hate set screws.
Better off with a tapered collet, or a clamp hub or a taper pin.
Dave
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Thanks to everyone who responded with the great information and advise!
I will either use just one set screw, or go with two at 90 degrees as advised.
It never ceases to amaze me how much knowledge is represented on this forum. And how ready and willing people are to share it! :)
Thanks everyone!
Kim
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If You think 2 setscrews in one hole are a pain, just wait until someone brings in a rush job pulley to be rebored and leaves one in the hole. :o
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If You think 2 setscrews in one hole are a pain, just wait until someone brings in a rush job pulley to be rebored and leaves one in the hole. :o
Did I mention I hate set screws?
8)
If you ever get a chance to use these....go for it.
http://www.fennerdrives.com/trantorque/
Dave
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Whilst on the subject of the little buggers, I've had several of the smaller sizes round out. A couple were on my last build and some were in , shall we say, Asian built tooling. I've replaced the ones in the tooling with some from the auto parts store and made some square head bolts for my build. Are a lot of the "supplied stuff" just that cheap and soft?
Whiskey
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Did I mention I hate set screws?
8)
If you ever get a chance to use these....go for it.
http://www.fennerdrives.com/trantorque/
Dave
I agree completely, I also hate set screws. This particularly for withstanding torque. I have used set screws bearing on top of a key. This works well to keep the "thing" from moving sideways but the key takes the torque. Most commercial sprockets I've seen come with two set screws at 90deg, one on top of the keyway. I've typically left the second set screw out, only the one over the key. Thus, if the set screw leaves a ding, it does so on the replaceable key not in the shaft. If one dings the shaft it makes removal harder. Can also file or machine a flat on the shaft for a set screw, then the ding is below the shaft diameter. But I'm with Dave, I hate set screws.Set screws work even less well on hardened shafts.
Tapered bushings (QD type) work very well, with or without a key. I haven't seen any small sizes though. I've also used the Fenner Transtorque that Dave mentioned. They work very well and only require a straight shaft and a straight bore. They're available at least down to 1/4" bore, but they are expensive. The 1/4" bore from MSC (USA) is $50. On larger stuff I've used a split collar with a bolt pattern machined into it. The bolt pattern holds the split collar to the hub to be restrained. Not as good as a key, but OK.
I've been considering what to use for model engines. I'd love to use Transtorques but can't justify the cost for a hobby. Maybe try to machine up a taper lock hub. Oh, I also hate pins holding a hub to a shaft, particularly if it's not meant to be permanent.
That's my story and I'm sticking to it. Thanks.
Hugh
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I have no problem with set screws. I learned as an apprentice many many years ago to use two set screws at 90 degrees. I find the biggest problem with small set screws as used on model engines, is that either the hex hole in the set screw rounds out, or the hex wrench itself rounds off on the end. (even the expensive ones).
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FYI
I started looking around and found two sources for small "taper bushings", in addition to Transtorque. Stock Drive Products (https://sdp-si.com/eStore/Catalog) (search for "taper bushings") has some. Also Econobelt.com (http://www.econobelt.com/Q460/RFQ/Pg_1-251.html). Both tend towards metric (yuck) but Econobelt has some small inch versions stuck into the list. About half the cost of Transtorque. These look simple enough to machine at home, much simpler than the Transtorque system. They also work with a straight bore and round shafting. I'm not sure how they are released though. They are small, so maybe a small hammer? :-)
Hugh
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I'm a member of the set screw haters club too, install on top of a keyway works OK. There are many ways to hold flywheels to shafts that hold tightly & are cleanly removable without all the aggravation of slipping flywheels, burred shafts, rounded hex wrenches & spilt or rounded set screws. Yes set screws are one of my peeves. Gary
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I appear to be the one out here......... :facepalm: & this is a little off thread but still relates to HPGS & SHCS
1. Following costly hydraulic cylinder failures, our Australian steel industry studies in 2012 confirmed that there was no recognised or accepted [A&NZ, British, ANSI or DIN Standard] for the nomination of Scotch Keys .. [being hollow pointed grub screws], their sizing or positioning
2. Installing two HPGS @ 90 degrees to a component on a shaft is only guaranteed to off set the diametrical clearance to the greatest deviation
HPGS are a necessary component element in engineering...if they are sized & installed correctly :hammerbash: they will not fail ............Derek
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And they bugger up the shaft when they loosen....and they do loosen...and getting them apart after the shaft is buggered up is miserable......and I've yet in 30 years of designing all kinds of equipment from boom trucks, implantable medical devices, machine tools and automated test handlers and extruders for fiber optics.... I've yet to see one that works half as well as was desired!...and never as well as a taper collet or a taper pin, or a clamp collar..or a living hinge.....or just about ANY other solution...other than a set screw!... :hammerbash:
Other than that I have no strong feelings on the matter.....
.,.....Did I mention I hate setscrews? 8)
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And yes you can make small taper collets...this one for my Seadog.
(http://i164.photobucket.com/albums/u27/mcandrew1894/Seadog%20build/P2070034_zpsec11c7d6-1.jpg) (http://s164.photobucket.com/user/mcandrew1894/media/Seadog%20build/P2070034_zpsec11c7d6-1.jpg.html)
That's the camshaft gear....and once on ....ITS ON.
The angle is 10 degrees included.....it's a copy of a ETW design.
Dave