View Full Version : Machining Oarlock Shafts
11-22-2002, 01:26 PM
This is something I have just been curious about for a long time...
When you look at an oarlock it seems clear that the shaft has to be machined on a lathe to get anything like a decently smooth and true surface. What I can't figure out is how the heck does one mount the oarlock on a lathe to do the truing? I'm sure someplace that's making hundreds or thousands of them (like Wilcox Crittendon) would probably have a special jig all set up, but say someone like me wanted to have just a few oarlocks made to a special pattern, it doesn't seem like any of the stand lathe chucks I've seen would get very far with holding an oarlock???
The best I can think of is an offset plate with a shaft to mount into a 3-jaw chuck and some pins and screws on the plate to position and hold the oarlock in place, but it seems like their should be an easier solution.
11-22-2002, 01:55 PM
In a drill press, drill a small center hole in both ends of the shaft. Now you can turn the lock between centers. I can think of other ways but this would be the easiest.
11-22-2002, 01:58 PM
It's cast and then cleaned up. There are machine lathes that have moving cutters to go around a stationary piece, but that precision is not utilized in oarlocks.
11-22-2002, 02:06 PM
Metal Lathes have 3 and 4 jaw scroll jaw chucks.
In a 4 jaw chuck back off 2 of the jaws and grip the horns in the other 2 and advance cutter to clean up castings. A good workman can do almost as good with a polishing lathe or a belt grinder.
The oarlock shaft is not 'tits on' for accuracy so I doubt it goes much beyond the polishing lathe/belt grinder/buffer stage.
11-22-2002, 02:51 PM
One of my old books has a section on turning a taper on a metal lathe. I'll have to check it when I get home to see how the piece is chucked. The method has to do with moving the tail off center. It may be that the piece turns on two pin centers and is driven with a dog, unless there is some type of "U Joint" adapter for the purpose.
11-22-2002, 03:04 PM
Taper attachments for metal working lathes are a very expensive accessory. Tail stock is set over according to scale on attachment.
Doubt very much if commercial oarlocks are made this way. Good patterns, a method of taking off any 'flash'and a polish, its done. 'Flash' can also be removed in a tumbler.
11-22-2002, 03:41 PM
I don't know how the big boys would do it but if I were to cast my own oarlocks I would make the shaft a bit longer than necessary. Use the chuck to grab the shaft, not the horns, and machine it. When you're done cut off the excess bit of shaft either with a cut-off tool right on the lathe or with a saw off the lathe. Use, a live center, low rpm's and watch your fingers.
[ 11-22-2002, 04:42 PM: Message edited by: James R ]
11-22-2002, 03:45 PM
Interesting. All sorts of ideas. I have seen oarklocks with a little dimple at the bottom of the horns -- which would match with turning them between centers.
I thought about a 4 jaw chuck but it didn't seem like that would be a stable enough 'grab' since you would just be grabbing the tips of the horns...but maybe that would do it. Hey, what about a four jaw chuck with the tailstock brought up so that it engages with the end of the shaft.
The bronze WC oarlocks I have sitting around (which I consider to be sort of mid-range oarlocks in terms of quality) were definitely trued up on a lathe, but they certainly aren't tapered and they don't have a dimple. Here is a somewhat crude scan of one:
If it were me and I was only machining 1 set, I would find a tin can that fits the upper half of the oarlock and cast a low melting point bismuth alloy into the cavity between the can and horn. Remove the can with a die grinder or hacksaw. Chuck the rough cast oarlock shaft up in a 3 or 6 jaw lathe chuck and turn the bismuth casting concentric to the shaft. Careful not to go too deep and hit the horns. Now reverse the part and turn the shaft to your desired diameter. When you're happy with the results, melt off the bismuth and admire your work!
11-22-2002, 07:08 PM
Bruce: I checked my "How to Run A Lathe" 33 rd Edition from South Bend Lathe.
".. primarily intended to assist the mechanic and machinist in the care and operation of the South Bend Back-Geared Screw Cutting Precision Lathe. However, the book will also be found helpful to any mechanic..."
They do indeed show turning a taper using an offset tail, and turning between two point centers. They don't show or say anything specifiec about how to drive the work. In the section on "Proper Placement of Dogs", they caution not to let the tail of the dog rest at the bottom of the faceplate slot. Presumably to allow it to move if the work is not precesely alligned (intentionally or otherwise). They also say that for severe or short tapers the compound tool holder should be used. With care you could cut short sections of taper according to how much screw you have in the compound rest.
They show an attachment for turning tapers that is an exotic tool rest on angles slides, operating with a centered tail pin and a regular jaw.
I'm not sure how good this advice will be. The book only cost 25 cents (in 1937).
Peter Malcolm Jardine
11-22-2002, 10:12 PM
I think the four jaw chuck with the tailstock brought up is probably the most sensible. If your two jaws won't advance far enough, make up a small set of fitted blocks for the two jaws that need to clamp in farther. Bronze is pretty soft so if you take your time cutting, you should be okay with that rig. One of the problems I have found with bronze is that its hard to get a consistently hard cast that will stand up without making the size of the cast fairly bulky. I didn't have a motorboat until I was in my teens. Rowed all the damn time since I was five (and loved it! :D )But I broke oarlocks fairly often. I have often thought you could make up a set of hoop oarlocks in hard stainless, with a flatbar hoop and a machined pin that would be really strong... but then again I have a set of english oarlocks in galvanized that must be forged or something cuz I have never put a dent in them for more than 25 years. Hey.. what happened to wooden pins?
11-23-2002, 12:29 AM
Probably a small boring machine or mid-sized drill press with a fixture to hold the rowlock and a specially made tool (like a tenon cutter) to machine the shank. You run 100s of these at a time - you're not going to waste a lathe setup on them, which takes a minute or two to lock the piece and run the taper, when a vertical spindle machine will do it in 3-5 seconds.
11-23-2002, 01:40 AM
What Dave said. You don't need a machine fit. Do it on a belt grinder.
11-23-2002, 07:54 AM
I've turned some for a local builder. He has them cast with the shank extending past the horns. I chuck up the part on the horn side and turn the shank down to size. Afterward I just cut off the part I chucked and he gives it back to the foundery when he has the next batch cast.
11-25-2002, 02:52 PM
Well, a topic I think I am close to. I started as a machinist in my youthful days and I tip my hat to James and holzbt. Yes the longer than required shaft is one way but I would have a tailstock center pressed into the bottom of the yoke to just steady the piece. I would use a live center but in a pinch the dead center will do.Holzbt has an interesting way of approaching the problem and I like the "outside the box" approach. My slant would be to use an extnded dead center in the lathe chuck and reach into the yoke on to a small indent. At the other end I would have my live center in the tailstock. Now you have the oarlock supported and would fabricated a dog to clamp onto the yoke and drive against one of the chuck jaws. Any questions? As for the production method, ther would be a dedicated lathe that would be set up to do the work of that specific oarlock design.
11-26-2002, 10:19 PM
Thanks for all the ideas! Quite a range of ways to go at this...
I have been contemplating various ideas for oarlocks and this was the one piece that had me somewhat puzzled.
11-29-2002, 06:57 PM
I have a bunch of oarlocks of different brands. I think Dave F. is right, since very few of them show signs of having their shafts machined--only cleaned up a bit, probably with abrasives, and polished.
Powered by vBulletin® Version 4.2.1 Copyright © 2013 vBulletin Solutions, Inc. All rights reserved.