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11-10-2007, 12:01 AM #1
i have a connecting rod (crank arm), that had its bore worn out. i bored it oversized with a boring head, and installed a (sae 660) bronze bearing with a press fit. a new spindle was also made to replace the old one.
my (very limited) understanding of bronze bearings is that under the following circumstances you must add an oil groove:
if the circumfrance of the bearing is > 1.0 inches (oil will travel in a un-grooved bearing only 0.5 inches axially in each direction from the oil hole)
the specifications for the oil groove are:
a. 1/16"deep, or 1/3 the wall thickness.
b. 1/8" wide
c. terminating not closer than 1/8", or (.05 x length of bearing) to end of bearing.
the thickness of the bronze bearing is .090", the diameter of the spindle (shown in photo) is 1 1/4 inches. the length of the spindle is 2 1/4 inches. the target rpm is below 100 rpm, and will have extremely heavy shock loads (its part of a planer).
my conclusion of the above, is that i must add an oil-groove (due to width of bearing), and it also must be helical (circumfrance of bearing is > 3", oil will only travel 1").
depth of oil-groove should be .030"
uh, is my assesment of the above correct?
can anyone reccomend a procedure to cut an internal helix in a bronze bearing (this will be my first helix).
11-10-2007, 12:10 AM #2
That is a very commendable goal. Special machines were made to do this. As a youngster, I had seen them in action at older engine repair shops. Tobin Arp comes to mind.
A lathe makes a halfway decent groover. I just used to select the lowest spindle speed and the fastest lead. Not to spec of course, but lots better than no groove.
I have seen MANY grooves that were put in by hand with such as a cape chisel. An "X" centered on the oil port sure isn't healical, but will get the job done.
11-10-2007, 12:16 AM #3
first off we can tell from the pics that this is not a extreme heat or High-speed rotational useage application.
A helical oil groove would work great and look really pretty.
The amount of working surface that the bearing you have can be done by scraping (4) vertical grooves (90* apart) and connecting them with a horizontal oil groove centralized in the bearing.
I'd draw you a picture if I thought it would help, but most of the people on here are elitists who frown on helping those who are as they refer to You and I as NON....Ahem...NON White". BTW the guy that posted before us is a clown, and most likely a racist too, But we cuts metal all the day long.
11-10-2007, 02:42 AM #4
1-McMaster Carr and others-sell grooved bushings
2-In a pinch, I've taken small HSS or carbide ball burr in high speed grinder, and hand cut grooving for low speed, high pressure application, just like u'r doing.
JC Watts plays THE RACE CARD....."but most of the people on here are elitists who frown on helping those who are as they refer to You and I as NON....Ahem...NON White". BTW the guy that posted before us is a clown, and most likely a racist too, But we cuts metal all the day long."
You know JC--I'm a new member and didn't subscribe becuz I thought I was joining a bunch of cracker elitists, 'minority activists', or various racial profiling, insulting, etc.
....and I doubt that any other members joined for those reasons--which should be apparent in the tenor of this forum.
An apology and retraction of your shoot-from-the-mouth statements is due from you--Sir!
11-10-2007, 03:04 AM #5I'd draw you a picture if I thought it would help, but most of the people on here are elitists who frown on helping those who are as they refer to You and I as NON....Ahem...NON White". BTW the guy that posted before us is a clown, and most likely a racist too, But we cuts metal all the day long.
11-10-2007, 04:46 AM #6
How about you chuck the bushing up and turn a internal 4 tpi thread .030 deep then take out bushing turn it around and thread another 4 tpi .030 deep
11-10-2007, 06:14 AM #7
We used to do them like John O suggests with a cape chisel.
11-10-2007, 07:20 AM #8
Huh, I just posed this same question to my instructor. An old motorbike I'm restoring uses these for swingarm bushings. His suggestion was essentially the same as LukeA's. Treat the groove as an internal thread and do it on the lathe.
Now of course I haven't done it, seeing as I haven't learned how to cut threads yet. But it seems logical to me.
11-10-2007, 10:36 AM #9
Quite a while ago i was reading an article about the quorn cutter grinder (at least i think it was the quorn) now the verticle post had a real coarse thread on it that was said to be produced by figuring out gearing for a really long lead, then driving the lathe from the leadscrew to keep speed under control. i figures this would work at a pinch if set up for 1 tpi or similar, of course being that coarse and only in bronze and shallow you could run the lathe by "hand power"
11-10-2007, 10:53 AM #10
If you are tempted by the 'lathe set to 1 TPI' method make sure you grind the tool correctly as you will need a large amount of relief to stop the back edges of the tool fouling the freshly cut groove.
But you should'nt need to go that deep.
<<used to make aircraft fuel pump bearings in metallised carbon that needed that sort of lube grooves in them
11-10-2007, 11:08 AM #11
LukeA nailed the easiest way to do them and make them look decent.
I use a stout threading bar with a radius tool instead of a 60 deg. threader, works great. I have cut them in 4140 PH and lots of bronze like that.
11-10-2007, 11:30 AM #12
This is a rpoblem that has come up again and again. If you check with the lube folks you will find out that grooves were put in way back before high film strength oils were developed. Any grooves installed since the '50s are just by habit.
I have a lot of bushings out there running without oil grooves. Some have been in daily use for 30 years. If the bearing requires replacement after 50 years then I will not see it again for another 20 years if I'm still arround.
11-10-2007, 12:06 PM #13
We called those "slingers". Always hated doing them. The first few I did looked pretty shakey. After half a dozen or so, got the hang of it. All the tool geometry suggestions are dead on from my experience. We did them by hand, on the lathe, at low rpm feeding by hand. Mostly in brass and a few in steel, re-building impeller pumps. Single Helix to a groove and also a double helix. I would think, with CNC's, it would be a very easy task now.
11-10-2007, 12:11 PM #14
I did a "Quick 'n Dirty" helical oil groove job for a friend's motorcycle swingarm replacement bushings using an abrasive fiber disc held in a Dremel tool. Not pretty or particularly smooth, but a light pass with some 400 grit sandpaper on a wooden dowel cleaned it up nicely.
11-10-2007, 01:12 PM #15
Whats this crap from JC Watts?!?!? My friend you are way WAY out of line. Not only that but your comments are a total surprise considering that you are normally a very helpful and knowledgeable poster.
11-10-2007, 02:15 PM #16
There's almost as much bull**** circulated about the efficacy of oil distribution grooves as there is on flaking and frosting. I've seen grown men of long experience almost come to blows over the merits of a figure eight oil groove vs the helical groove Vs the classic "X" while completely neglecting the orientation of the oil feed to the load the bearing was intended to restrain on an acis of rotation.
All that said I strongly suggest anyone having to replace/restore bushings consider their means of lubrication to the vector of the applied load, the speed, service, cyclic operation, type of lubricant, load reversals, and other factors AND consider whether an oil groove is indicated or not.
A plain bearing depends on the hydrodynamic pumping action of a journal rotating in a bearing. The rotation fo the journal draws lubricant into the clearance space to form a loaded film. The film is continuosly replentished by the journal rotation and because the lubricant is free to ooze at the ends of the joiurnal the pressure falls off towards any interruption permitting an oil escape. This film covered an area whose localised pressure distribution is someting like that of a weather disturbance and can indeed be described in terms of coutrours of constant pressure. So long as the film is maintained metal to metal contact is prevented.
As with everything in any human activity, one must balance conflicting needs, that is, ensure lubrication without compromising the efficacy of the bearing film. Lubricant distribution grooves supply lubricant essential to a film forming bearing. If misplaced, they also interrupt it.
There are no hard and fast rules regarding the placement of oil grooves except not to place them in the loaded film area of the bearing. If one wishes to determine the best place for oil grooves he must first determine the direction of the applied load.
Take a connecting rod for example. Its load is predominately axial transmitting the forces of the machine elements it connects and its own weight is usually a small fraction of the transmitted load. Consider also the orientation of the connecting rod bearing to its lubricating port. Quite often the port is concentric to the working load and the presence of the port is centered in the area of the loaded film. In automotive engines the oil distribution groove is annular and the bearing is designed with this interruption in mind.
To make an oiling port in line with the loaded bearing then make it the nexus of a complicated oil groove is sure to shorten the life of the bearing. Only the man on the job and or the expertise he consults with can determine the many factors and arrive at a design of lubricant introduction and distribution that maximizes bearing life and service and minimizes the effect of bearing design elements on its ability to function. The rule mentioned by the original post are not hard and fast. They might be regarded ad rules of thumb and if other factors are correctly balanced they may be "Bent" considerably.
Much depends on the load and the whether the lubricant is pressureised. Generally when it comes to oil grooves, simpler is better.
Once the need and a design is determined how to make an internal oil groove has to be considered. For small lots the groove can be cut with ball burrs in a hand held rotary tool following a felt tip mark is about the simplest. Simple jigging and "peg in a groove" motion guidance can produce quick, efficient oil distribition groooves in signifcant quantity before the purpose built equipment and farmout to specialty houses overtakes the simpler process.
Consider for example, a used up Monoset tool grinder as an oil groove cutter. Collet the work in the work spindle, set the sine bar to the helix, and mount a ball end cutter in the wheel spindle.
11-10-2007, 04:20 PM #17
If you cut a piece of plastic or shim stock and insert it into the bore and angle it, you could use it to draw a helix with a sharpie and then use a dremel with a ball cutter freehand.
BTW, what is this for? Old engine?
11-10-2007, 04:39 PM #18
isn't there anyway you could substitute a change gear so that it makes a thread lower than the lowest that was there before ...
and then turn a handle in the headstock.
or am i missing something here.
all the best.mark
11-11-2007, 01:18 AM #19
If that's a multi cylinder you're working on keep in mind that you're changing the weight and balance of that rod.Hone bushing to size after press fit and oil grooving.
11-11-2007, 03:21 AM #20
i appreciate everyones assistance, and help.
well, i attempted to scrape the helix.
it did'nt work too good, i had dificulty with the angles, and the tools that i had to work on it. i made 2 tools; one of 1/8" square steel (i tried to harden, and temper it, but the propane bottle leaked, caught on fire, and i decided to not continue with scary fires) , the other about 1/8" round steel. i had another tool, shaped like a gouge 1/4" wide, bent at an angle: this angle helped with the inside curve of the bearing.
here are some photos of this:
i scraped a horizontal groove running from the oil fill hole (1/8" in diameter) to 1/8" short of each end of bearing (i'm not sure if the diameter is large enough).
next i found 3 applicable oil cups, selected and installed the small one (i am concerned that the glass one will break under high speeds).
i installed the connecting rod in the planer:
continued in next post