Bushes and Bearings

[Shamal]

Hi everybody peeps

Not really thought about it before but what are the pros and cons as regards bearings versus bushings?

Enlighten me oh wondrous ones and Skara lol.

Regards 

[Iceni]

Bushings can't collapse but run with slightly higher friction. They wear out rather than collapse.

Bearings run with less friction, They can and do collapse, They can also allow for an ingress of dirt that can shorten the lifespan and increase your service period.


Both have advantages. Both have disadvantages.

You can make a bushing build run at 25rps without any issues so for me I'm a bushing guy. As the increased service period is more important to me than reducing friction.

[Shamal]

1 hour ago, Iceni said:

Bushings can't collapse but run with slightly higher friction. They wear out rather than collapse.

Bearings run with less friction, They can and do collapse, They can also allow for an ingress of dirt that can shorten the lifespan and increase your service period.


Both have advantages. Both have disadvantages.

You can make a bushing build run at 25rps without any issues so for me I'm a bushing guy. As the increased service period is more important to me than reducing friction.

Hi @Iceni 

Thanks for that. See what you mean. Do bearings run quieter though.👍

Regards 

[Adolf Hamster]

pretty much as above.

 

bushings can tend to wear in a single direction (the hole goes from round to oval) but that's a gradual failure rather than bearing's preference for sudden catastrophic failure.

 

if i'm mixing types i tend to go for bushings towards the sector (highest impact loading) and bearings towards the bevel (highest rpm)

[Shamal]

3 minutes ago, Adolf Hamster said:

pretty much as above.

 

bushings can tend to wear in a single direction (the hole goes from round to oval) but that's a gradual failure rather than bearing's preference for sudden catastrophic failure.

 

if i'm mixing types i tend to go for bushings towards the sector (highest impact loading) and bearings towards the bevel (highest rpm)

Ok. Good tips there. Thanks 🙂

[Sitting Duck]

Yes bearings are quieter - than dry bushings

when shimming/spinning "dry" bushings you can get a squeak as you spin

(drop a bit of oil/silicone on them to shut them up whilst testing)

 

Once shimmed up - you coat them to bits and slap it all together

 

bearings spin a bit longer on bearings - but any minor drag difference is nothing

(compared to strain from spring etc... when in actual use)

 

What some people do in some/certain cases is do a mix of bushings/bearings

 

the most important point is a bushing UNDER THE SPUR as this seems to be a stress point

where energy from bevel's 10 teeth to SPUR to sector - right in the middle the strain increases under spur

 

G&G bronze bushings for example wear extremely quick - rool smooth but wear out fucking quick

this is known point for G&G bushings to wear to excess and once this becomes great, excessive play

will lead to failure at some point...

Other bushings will wear - maybe the bevel, sector seems to be quite long lasting

(sector rotates the very least of all gears, even though the spring's tension is exterted upon it)

 

It is UNDER THE SPUR that you should or highly recommended to run on bushings

even hard as nails super duper ceramic's can fail under the spur gear...

 

 

 

I recommend a bushing under the spur

on top of spur - you can run a bearing, particularly if shimming room is tight

(I've had this on a very chunky 13:1 set, too tight on all bushing spur, but just got away with bearing on top

 

What you do to the other 2 x gears is up to you...

 

Now remember that bearings under the spur & sector can/could impede slightly on the selector plate

(on some large chunky bearings with some selector plates - others no issue)

So for that reason...

Bushing UNDER SPUR

&

Bushing UNDER SECTOR

(as bushings tend to be less raised externally than bearings - but are raised internally more

so less shims inside as a general rule on bushings (or slightly more if using bearings)

 

So Bushings under spur & sector

(a rough guide is say 0.2mm shim under spur & say 0.25mm under sector)

 

I personally would use a bushing ON TOP of bevel as the pinion is trying to throw the bevel into bushing

(me personally a bearing can be trashed if you drive the pinion/bevel heavily into the gearbox casing)

 

As the bevel spins 4.25 ~ 6.25 times to one revolution of sector gear...

I have used a bearing UNDER bevel if I was unhappy with sqeaky/tight/loose bushing under bevel

(place bushing/bearing onto gear axle and wiggle/check for excessive play)

some axles are 2.95mm & others just a whisker over 3mm

& certain bearings/bushings may be worn or made to shit tolerances

so don't fit sloppy bearings/bushings if you can help it

(of course just ignore this bit if you do not suffer with excessive OCD like moi)

 

anyway....

 

I would fit a bushing under spur & under sector

(keep it similar for shimming underneath & selector plate issues)

PLUS - also a bushing ON TOP OF BEVEL for durability & if I wind the motor in too far

 

that is 3 out of 6 - the last 3 is up to you and what the situation dictates...

 

a bearing under the bevel is viable - but not maybe if build a stressy snappy build

 

a bearing on top of spur is fine - very little stress there unlike underneath the spur

(will help it rotate a tiny bit smoother)

 

a bearing on top of sector is an option, but really the sector rotates once to 4~6 bevel turns

(and about 1.75 turns of spur but varies on gear ratio being used, but spins less by comparison)

 

ONE POINT - when using bearings on top of spur/sector...

on v3 AK's for example, check to ensure the more protruding bearings do not foul or impede the linkage in use

they shouldn't but if using a chunky bearing on a v3, I noticed I needed to smooth AK linage a tiny bit

so it glided over the bearing on top of spur gear

(very very slight risk of catching, was very close but cleared after a light smoothing of underside of linkage)

 

So EVERY instance is slightly different, the spec of the build, the different ways that SOME cases bearings may snag

& other cases, bearings will clear fine as some selectors often have minor recesses to avoid bearings catching

(not all are like this)

 

Depends on how chunky the gears are - 13:1's especially SHS's can be fucking chunky

 

I'll use all 6 bushings mostly

with the odd bearing if required (chunky spur gear, so on TOP of SPUR)

maybe 50/50 mix if a std 18:1 build & say I can find 3 good bearings with little wear/play in original box

(in have them to hand - otherwise, fuck it I'll chuck in mostly bushings and be done with it)

 

BUT - it really depends on the box in front of you and what shit fits best

plus you go on your gut instinct

 

Bushings are thicker on inside - so slightly less shimming required/available

 

Bearings are usually more exposed externally and in some cases can risk fouling/impeding on selector plate/mechanisms

(plus need a bit more shimming internally usually, some might say you have a bit more room flexibility to work with - nah)

 

THERE IS NO RULE BOOK - well not really, bushings are durable

but anything shimmed badly will tear itself apart sooner - so it is YOUR CHOICE & attention to detail in the end

[Shamal]

14 minutes ago, Sitting Duck said:

Yes bearings are quieter - than dry bushings

when shimming/spinning "dry" bushings you can get a squeak as you spin

(drop a bit of oil/silicone on them to shut them up whilst testing)

 

Once shimmed up - you coat them to bits and slap it all together

 

bearings spin a bit longer on bearings - but any minor drag difference is nothing

(compared to strain from spring etc... when in actual use)

 

What some people do in some/certain cases is do a mix of bushings/bearings

 

the most important point is a bushing UNDER THE SPUR as this seems to be a stress point

where energy from bevel's 10 teeth to SPUR to sector - right in the middle the strain increases under spur

 

G&G bronze bushings for example wear extremely quick - rool smooth but wear out fucking quick

this is known point for G&G bushings to wear to excess and once this becomes great, excessive play

will lead to failure at some point...

Other bushings will wear - maybe the bevel, sector seems to be quite long lasting

(sector rotates the very least of all gears, even though the spring's tension is exterted upon it)

 

It is UNDER THE SPUR that you should or highly recommended to run on bushings

even hard as nails super duper ceramic's can fail under the spur gear...

 

 

 

I recommend a bushing under the spur

on top of spur - you can run a bearing, particularly if shimming room is tight

(I've had this on a very chunky 13:1 set, too tight on all bushing spur, but just got away with bearing on top

 

What you do to the other 2 x gears is up to you...

 

Now remember that bearings under the spur & sector can/could impede slightly on the selector plate

(on some large chunky bearings with some selector plates - others no issue)

So for that reason...

Bushing UNDER SPUR

&

Bushing UNDER SECTOR

(as bushings tend to be less raised externally than bearings - but are raised internally more

so less shims inside as a general rule on bushings (or slightly more if using bearings)

 

So Bushings under spur & sector

(a rough guide is say 0.2mm shim under spur & say 0.25mm under sector)

 

I personally would use a bushing ON TOP of bevel as the pinion is trying to throw the bevel into bushing

(me personally a bearing can be trashed if you drive the pinion/bevel heavily into the gearbox casing)

 

As the bevel spins 4.25 ~ 6.25 times to one revolution of sector gear...

I have used a bearing UNDER bevel if I was unhappy with sqeaky/tight/loose bushing under bevel

(place bushing/bearing onto gear axle and wiggle/check for excessive play)

some axles are 2.95mm & others just a whisker over 3mm

& certain bearings/bushings may be worn or made to shit tolerances

so don't fit sloppy bearings/bushings if you can help it

(of course just ignore this bit if you do not suffer with excessive OCD like moi)

 

anyway....

 

I would fit a bushing under spur & under sector

(keep it similar for shimming underneath & selector plate issues)

PLUS - also a bushing ON TOP OF BEVEL for durability & if I wind the motor in too far

 

that is 3 out of 6 - the last 3 is up to you and what the situation dictates...

 

a bearing under the bevel is viable - but not maybe if build a stressy snappy build

 

a bearing on top of spur is fine - very little stress there unlike underneath the spur

(will help it rotate a tiny bit smoother)

 

a bearing on top of sector is an option, but really the sector rotates once to 4~6 bevel turns

(and about 1.75 turns of spur but varies on gear ratio being used, but spins less by comparison)

 

ONE POINT - when using bearings on top of spur/sector...

on v3 AK's for example, check to ensure the more protruding bearings do not foul or impede the linkage in use

they shouldn't but if using a chunky bearing on a v3, I noticed I needed to smooth AK linage a tiny bit

so it glided over the bearing on top of spur gear

(very very slight risk of catching, was very close but cleared after a light smoothing of underside of linkage)

 

So EVERY instance is slightly different, the spec of the build, the different ways that SOME cases bearings may snag

& other cases, bearings will clear fine as some selectors often have minor recesses to avoid bearings catching

(not all are like this)

 

Depends on how chunky the gears are - 13:1's especially SHS's can be fucking chunky

 

I'll use all 6 bushings mostly

with the odd bearing if required (chunky spur gear, so on TOP of SPUR)

maybe 50/50 mix if a std 18:1 build & say I can find 3 good bearings with little wear/play in original box

(in have them to hand - otherwise, fuck it I'll chuck in mostly bushings and be done with it)

 

BUT - it really depends on the box in front of you and what shit fits best

plus you go on your gut instinct

 

Bushings are thicker on inside - so slightly less shimming required/available

 

Bearings are usually more exposed externally and in some cases can risk fouling/impeding on selector plate/mechanisms

(plus need a bit more shimming internally usually, some might say you have a bit more room flexibility to work with - nah)

 

THERE IS NO RULE BOOK - well not really, bushings are durable

but anything shimmed badly will tear itself apart sooner - so it is YOUR CHOICE & attention to detail in the end

Wow! Great explanation thanks.will read properly in bed.lol

I have taken apart ameoba 013 box cause she would fire five times and then stop until batt was disconnected and then it.would fire five times again.

I have cleaned gearbox up and checked all gears which all look good.bushings however keep falling out.are they supposed to be a push fit?

 

[Sitting Duck]

is why bushings in gearboxes

& metal rack on pistons are epoxy'd in

 

pop into poundland, buy a cheap £1 syringey 2-part epoxy

(wipe sides of box/bushings clean)

squeeze out same amount 2 moderate size blobs

mix with matchstick and smear a small amount on the inner rim of case

push them in and leave to set for a few hours

 

wipe off any excess & you should be able to set all 6 in one sitting if you move briskly

(the epoxy tends to set within 5 mins)

 

sorted

 

not watched vid - got guests over

but this cheap shit will do the job for a quid

 

 

JB Weld is for more robust jobs, but just getting stuff to stay put

well I use this quite often for bushings & piston racks

(plus other stuff)

[Shamal]

18 hours ago, Sitting Duck said:

is why bushings in gearboxes

& metal rack on pistons are epoxy'd in

 

pop into poundland, buy a cheap £1 syringey 2-part epoxy

(wipe sides of box/bushings clean)

squeeze out same amount 2 moderate size blobs

mix with matchstick and smear a small amount on the inner rim of case

push them in and leave to set for a few hours

 

wipe off any excess & you should be able to set all 6 in one sitting if you move briskly

(the epoxy tends to set within 5 mins)

 

sorted

 

not watched vid - got guests over

but this cheap shit will do the job for a quid

 

 

JB Weld is for more robust jobs, but just getting stuff to stay put

well I use this quite often for bushings & piston racks

(plus other stuff)

Hit our local poundland for the epoxy. Guess how much? Yep correct.One British pound.amazballs!

Blasted every thing off with easy start,not a speck of grease🙂.

Stuck bushings in and now waiting for it to stick.Luverly 👍

Regards 

[Lozart]

I can honestly say I've never yet seen a gearbox with bushings epoxied in place.

 

Should the gun last long enough to need them replacing you're stuffed!

[Davegolf]

Bearings offer less rotating resistance, but ideally need the gear axles to be a tight fit into the inner race.

Ideally suited to low load / high RPM. - Spastic ROF builds

 

Bushings are a static item, the gear axle rotates in the bushing with a clearance for lubrication.

A Moly type grease is best for this application.

Ideally suited to higher loadings.

 

It is for this reason that bushings should be bonded into place, so they do not in turn rotate in the gearbox shell.

I use Loctite 270 for this purpose, if you need to remove them for whatever reason this easily done with the aid of a heatgun.

[Lozart]

@Davegolf I'm aware of the principle, I've just never seen any need to do it on an airsoft gun. Unless the gearbox shell or the bushings are a particularly bad fit then the friction fit itself should be enough to hold the bushings in place. Of course if the gear axles are binding in the bushing, causing it to rotate that's a whole different issue.

[Shamal]

7 hours ago, Lozart said:

I can honestly say I've never yet seen a gearbox with bushings epoxied in place.

 

Should the gun last long enough to need them replacing you're stuffed!

I think they will come out very easily. It's just to stop them rotating. It's a very thin film of 'glue'.

Bit like loctite really holds firm but not immovable when needs be.👍

Regards 

[Davegolf]

@Lozart I’ve only done it to precision bushings, most the stock ones are fairly sloppy and/or plastic.

 

By bonding them in perfectly square I can then hone the bushing ID so the axle fit is perfect.

Its also amazing how many gear sets axles are not actually round.

[Lozart]

14 hours ago, Shamal said:

I think they will come out very easily. It's just to stop them rotating. It's a very thin film of 'glue'.

Bit like loctite really holds firm but not immovable when needs be.👍

Regards 

 

For clarity - I have an engineering background and used to own motorcycles so the concepts of bearing fit and the difference between epoxy and Loctite are very familiar. For example - my old Suzuki had the left front wheel bearing held in place with Loctite because the previous owner had chosen to remove the coating from inside the bearing housing (I did eventually replace the wheel but hey, I was young and stupid). Ultimately if the bushing/bearing fits like a dick in a shirtsleeve then gluing it in is a band aid over an axe wound. The right answer is to get bearings/bushings that fit properly or replace the gearbox shell if the holes are off because they have worn. It's less of an issue with any sort of half decent bearing as the friction of the bearing to gearbox housing should easily overcome the friction in the bearing race (if it doesn't then you've either bought VERY cheap bearings, they just don't fit or the gearbox is screwed).

 

14 hours ago, Davegolf said:

@Lozart I’ve only done it to precision bushings, most the stock ones are fairly sloppy and/or plastic.

 

By bonding them in perfectly square I can then hone the bushing ID so the axle fit is perfect.

Its also amazing how many gear sets axles are not actually round.

 

When you look at the cost of most mainstream airsoft hardware it's a constant source of frustration/amusement that any of it fits together at all let alone with any degree of precision. If you're bonding in the bushings perfectly square and honing the ID to be perfectly round, how are you making sure that the gearbox halves are perfectly in line? If they're not then you're just making work for yourself, surely? It comes as no surprise whatsoever that the gear axles aren't round. I'm impressed if they're just the right length!

 

Don't misunderstand me here - I'm not saying that what you're doing is in any way wrong or that the engineering makes no sense, it's just that I don't see why you would want to in the first place. Yes, belt and braces engineering so that the 50p bushings last a bit longer in the £10 gearbox but none of what we're discussing here is to do with any sort of precision machine is it? Of course, I'm making the assumption that we're not trying to fit SiegeTek gears into a CNC billet gearbox here but we are talking about a system that relies on a floppy rubber O-ring on it's primary source of motive air to provide a dynamic seal...

 

None of which should stop anyone doing anything if the main justification is "because I can/want to". Fill your boots (just not with epoxy though, eh? That would be stupid).

 

 

 

[Sitting Duck]

To clarify the advice given....

 

The question was asked how to stop the bushings falling out ???

 

I gave the response to epoxy them in

& note a cheap Poundland epoxy rather than JB Weld or something

 

A light smear & I have been able to remove a couple of epoxied bushings easily

by a gentle tap - though there have been horror stories of cases cracking/chipping

when trying to remove an epoxied bushing (must have used industrial strength by the boat load)

 

The instance when a 13:1 spur was too thick to shim & had to place a bearing on top of spur

thus had to remove a bushing & replace with 8mm bearing instead

 

The expoxy suggested is hardly industrial strength & if a light blow failed to shift it

then place the casing in warm soapy water will assist its removal

 

If bearings/bushings or whatever are loose enough to fall out

then have fun trying to shim that box easily if they do not hold in place whilst pushing on axles etc...

 

Like correcting AoE, how much & what you use, ptfe for cylinder heads...

what wiring, mosfet/ECU system you use, your preferred motor/gear setup

along with your own personal rof, bb weight/mass - and fuck knows what else like brand of toy gun etc...

 

It is ALL down to your personal choice/preferences like nigh on most things in airsoft/life

 

What I do, is not gospel nor set in stone as I have altered & changed a number of things I do now

compared to say 6 years ago or even a few years ago, plus each box presents different issues

along with the various components that work/don't work as they should

 

If the replacement bearings/bushing fit snuggly there would be no real need to fix them in place

however as the old ones are removed, sometimes they needed a little coaxing to come out,

that in turn will add a little wear that even the exact same replacements may not fit quite as snug

as the originals did from the factory/sweat shop, so what to do if faced with loose bushings ???

(and the term loose is open to interpretation - if it is as loose as fuck then you need to try other bushings

or something before maybe looking for a new/less worn shell for example or some method to ensure centred

better before trying to affix them)

 

But loose bushings will make it a little awkward to shim up imho

and numerous people decide to epoxy them in if they are not quite a snug fit

others are dead set against it & that is fine it is their call/gun in the end

 

Same as epoxy-ing a steel rack in the piston, by default some pistons already come affixed/epoxied

sometimes they are affixed poorly, other times the rack comes out very easily - even quite loose in some

so when you might removed 2nd tooth you have the choice to refit or affix/epoxy the rack in like bushings

(call it peace of mind, call it what you will, but your call all the same)

 

The epoxy was a cheap mild glue & method to affix loose bushings & if done correctly can be removed OK

(an old chunky spur gear (top side), comes in handy to push in the bushings and to assist in removing old ones)

 

To each their own as they say, but I epoxy them in

and have been able to remove them without damage (when required)

 

I do not consider myself as the divine word on stuff, merely what stuff I do (at present)

and my own methods are constantly being reviewed & updated as I go

though I've been expoying stuff in where required for quite a while - my own personal choice btw

 

if bearings/bushing fit in all snuggly, then I probably wouldn't need to epoxy them

invariably I find in many cases they can fit in a little too easily & so I will add a smidge to hold them in place

(just so they stay put for shimming and not lift out still attached to gears when opening gearbox shell etc...)

 

Your gun/box - your choice as they say

 

 

[Davegolf]

Its all done in the name of convenience and consistency - you can take the thing apart repeatidly without thing fallin out that shouldnt, and shim readings are going to be repeatable.

 

Making sure that things that are not meant to move do not move - perfect fit seldom occurs in budget airsoft.

 

And yes i am talking about decent gearboxes and nice gear sets, even most mid range gearboxes have locating pins so once again you have consistency. Checking alignment is easy, bolt the gearbox halves together, use a dowel to check bushing hole squareness.

 

Basically if you are pressing bushings in, if they are made of plastics by pressing in you are deforming them to some degree, if they are metal you would likely be stressing the gearbox and/or not getting squareness of fit / alignment. Something has to give.

If you are using bearings the big relative clearances of the race will take up the lack of squareness / alignment.

 

TLDR - for an easy life bond your bushings in! - A perfect or slightly undersize bushing bonded in is better than interference fit from an engineering stand point with this being airsoft.

 

[Sitting Duck]

1 minute ago, Davegolf said:

 

Making sure that things that are not meant to move do not move - perfect fit seldom occurs in budget airsoft.

 

 

 

[Lozart]

All valid points. Personally I've never needed to fix bushings in, maybe I've just been lucky? 

 

Granted none of my guns ever gets used so much as to cause catastrophic wear and if we were talking about someone with only one gun that they're trying to make the absolute best they can for longest life and reliability then I get it. Thing is though, where does it stop? At what point  do you acquiesce to the law of diminishing returns? Most gearboxes do have locating lugs, granted but in the main they're cast from a shitty alloy to a budget and aren't great in terms of tolerances. Close enough really is good enough for the vast majority of cases in airsoft.

 

As for pressing in bearings, yes excessive force or too tight a fit will cause stress on the gearbox shell. A cheap/badly made gearbox might crack...eventually. Really shouldn't be an issue with a decent CNC aluminium gearbox though, plus you should be able to ensure you get high quality bearings/bushings designed to fit a precision machined hole. Granted there is a potential for the bearing to go in skewed as the  shell thickness isn't huge compared to the diameter of the bearings but there's just as much risk that a loose fitting bearing/bushing will be off centre if you glue it in.

 

Anyway, as with all things - your mileage may vary. I don't think you should need to glue in bearings/bushings but that's my opinion/experience.