Reaming, boring, press fit etc and pinning

[Andrew EvansParticipant @andrewevans67134]

I would like to get some advice and opinions – I have thrown all these subjects together as they relate to the job I am doing. I am currently building the Wyvern IC engine from the Hemmingways Kits castings. The job I am about to tackle is the crank shaft that is built up but I am not sure of the best way to tackle this. Others have reamed a hole in the crank web and used loctite, others have used a press fit and then brazed the joint with the shaft. There is also talk of pinning as well.

The crank shaft 0.5" diameter and annoyingly I don't have a 0.5" reamer nor do I have the equipment to braze parts as big as this (just a hand held gas torch and small hearth). My thoughts are to bore the hole in the crank webs to size in the lathe and just rely on high strength loctite. Is it worth buying a reamer just for this job, I also have to make the crank shaft bearings the same internal diameter of course?

Any advice would be greatly appreciated. Andy

[Andrew EvansParticipant @andrewevans67134]

[Roderick JenkinsParticipant @roderickjenkins93242]

Andy,

I, too, am making a Wyvern. I broached a similar question here. I decided to to go for Loctite only. As you will have made the whole thing yourself you can always go back and try something different if there is a failure of the joint. Loctite needs a bit of clearance but I have found that precision ground mild steel has sufficient clearance for the glue in a reamed mild steel hole. A reamed hole in bronze tends to be a bit tighter so this works for the bearings. You can, of course, bore all the holes to size but a reamer does make things easier.

Enjoy the build and keep us informed of progress.

cheers,

Rod

[JasonBModerator @jasonb]

My preferance on built up cranks is to bore, silversolder and then pin but you could substitute loctite for the solder. I've read of to many cranks failing on IC models that just had loctite. I also prefer to bore on the mill with a boring head which should make the two holes parallel to each other and you should be able to get the ctr distance more accurate than trying to pick up two punch marks on the faceplate or in the 4-jaw.

J

Edited By JasonB on 11/01/2014 13:17:10

[Rik ShawParticipant @rikshaw]

Andrew – I also am in the throws of manufacturing a twin throw crankshaft. Machine it from solid say some – I say life is to short wasting material and machining time trying to give birth to a crankshaft this way (I am talking smaller models here – big stuff is different). Fabrication for my smaller model is the way forward I have decided and although an elderly gent on one of the stands at the Sandown show cautioned against Loctite I firmly believe that a combination of Loctite and pinning will do the trick.

>Rik>

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Rik ,

Though often advocated Loctite AND pinning is ‘ Expert Model Engineer ‘ thinking – the Loctite either works or it doesn’t and the pin won’t make any difference either way .

Loctited shaft to coupling joints and similar assemblies in real engineering are normally just bonded .

Personally I’d just use a properly designed and made press fit if I couldn’t easily machine from solid .

Regards ,

MikeW

[Andrew EvansParticipant @andrewevans67134]

Many thanks all.

Rod – I have been following your build with interest, excellent work. I thought of doing a thread on my build but didn't want to steal your thunder – maybe i will do so – I have completed the bedplate so far.

I think i will experiment with scrap and loctite and see what force is needed to break a similar joint.

Pinning – I have never pinned anything, is it as simple as piece of silver steel loctited into a hole?

Press fitting – The few times I have tried it the fit has been too loose or too tight (resulting in the two pieces getting jammed). I don't have a press but have used the bench vice in the past. If i wanted to press fit a shaft in a 0.5" diameter hole what diameter would the shaft be?

Andy

[Roderick JenkinsParticipant @roderickjenkins93242]

Andy,

You're welcome to my thunder, no need to steal it. I, for one, would be very interested to see how somebody else does it.

cheers,

Rod

[Bill PudneyParticipant @billpudney37759]

If a Loctite joint is done properly it will be very robust. A long time ago I worked for Norton Villiers, who as some may recollect, used to make motorcycles.

The steering stem used to be brazed into the lower fork yoke. This was an expensive process. The suggestion was made to redesign the joint and use Loctite. There was a lot of tooth sucking and chin pulling, after all this is a critical joint, failure of which could result in death. So a series of trials were set up. When a push out trial was performed the Loctite did not fail, but the yoke material failed, it was, from memory cast iron.

All I can suggest is to go to the Loctite web site and get "full bottle". Then if you decide to use it, do it exactly i.a.w. the instructions, degreasing, cleaning etc. Many of the failed Loctite joints are the result of inadequate cleaning, and lack of instruction understanding.

No connection with Henkel, Loctite or any other similar firm.

cheers

Bill

[JasonBModerator @jasonb]

Andrew have a look at one of my crank shafts here , I prefer to pein over the end of a mild steel pin into a shallow CSK and then file flush as the result is almost invisible.

On of the reasons loctite joints on models fail is they are not withing the spec gap wise particularly when a beginner is trying it for the first time. eg the hole will be reamed (hopefully not drilled) and a bit of bar chosen that is the same nominal size. No account is taken for the tollerance of the reamer or actual size of the rod and how many use the correct cleaner.

J

[Bill PudneyParticipant @billpudney37759]

Posted by JasonB on 12/01/2014 07:56:00:

Andrew have a look at one of my crank shafts here , I prefer to pein over the end of a mild steel pin into a shallow CSK and then file flush as the result is almost invisible.

On of the reasons loctite joints on models fail is they are not withing the spec gap wise particularly when a beginner is trying it for the first time. eg the hole will be reamed (hopefully not drilled) and a bit of bar chosen that is the same nominal size. No account is taken for the tollerance of the reamer or actual size of the rod and how many use the correct cleaner.

J

Surely that's a failure of the person doing the job, not the product? We shouldn't blame the product for inadequacies of the user.

cheers

Bill

[Michael GilliganParticipant @michaelgilligan61133]

Andrew,

Loctite 638 High Strength Retainer [or equivalent] should do the job nicely, provided that the work is clean and the joint properly designed.

Have a look here

The link that I posted 21/04/2013 23:17:39  takes you to a Permabond document on Joint Design.

MichaelG.

.

Edit: Here is a useful guide from Loctite.

Edited By Michael Gilligan on 12/01/2014 08:58:27

Edited By Michael Gilligan on 12/01/2014 09:03:05

[Russell EberhardtParticipant @russelleberhardt48058]

Something that hasn't been mentioned is the temperature performance of structural adhesives. If you look at the data sheets you will see that the strength falls off significantly with increasing temperature. I don't know what temperature these little engines run at but to be on the safe side I would use a high temperature adhesive such as Loctite 648.

Don't ream, a slightly rougher finish is better, and make sure the parts are absolutely clean before gluing. I use acetone for cleaning but Loctite sell their own brand of cleaner/degreaser.

Russell.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Russell Eberhardt on 12/01/2014 09:40:22:

Something that hasn't been mentioned is the temperature performance of structural adhesives. If you look at the data sheets you will see that the strength falls off significantly with increasing temperature. I don't know what temperature these little engines run at but to be on the safe side I would use a high temperature adhesive such as Loctite 648.

.

Good point, Russell

Here is the [2004 vintage] datasheet for 638

Full strength up to about 50°C

… Temperature characteristic is roughly equivalent to Soft Solder

… but the overall performance is higher.

MichaelG.

[Anonymous]

Oh dear, I Loctited and pinned the crankshaft for my hit 'n' miss engine; that must make me a ex-spurt.

When I made the crank webs I started overlength and bolted them together before boring each set of holes on the lathe. It doesn't really matter if the throw is slightly off the drawing, as long as they're both the same. I left the appropriate clearance for the Loctite. I used silver steel for pinning, in reamed holes. I didn't countersink the holes, just left them as drilled and reamed. After finishing it it impossible to see the join. I chose this method as I ground the crankshaft and crankpin after rough machining, and I didn't want to spoil the finish by silver soldering.

Regards,

Andrew

[Andrew EvansParticipant @andrewevans67134]

Thanks all – I haven't had time to progress this yet as I got side tracked with something else (threading on CNC lathe). I am going to try a couple of suggested methods with scrap pieces first and go from there.

[Andrew EvansParticipant @andrewevans67134]

Tried loctite with and without knurling – on scrap pieces of steel. I used a 3/8" shaft in a hole drilled with a 3/8" drill. The fit was relatively loose on the unknurled section but needed pressing in after light knurling (diamond pattern – i don't have a straight knurl). Cleaned with isopropyl alchohol. Left to cure overnight and tested the strength with mole grips and the vice. Counter intuitively the knurled test piece could be moved but the unknurled piece couldn't be shifted even with maximum welly.

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