Roll pins - how useful are they?

[springcrocus]

This was brought into question in my "Calbourne" build log and I would rather that thread doesn't wander massively off track. Therefore, I have started this thread to discuss the use of roll pins and respectfully request that members don't clutter up "Calbourne".

For my part, I use them where I want to keep a joint from moving, rather than using a slightly looser joint and applying an adhesive. Also, roll pins are fairly tolerant of hole size and a drilled hole is usually sufficient, not needing a reamed hole.

Regards, Steve

[steamer5]

Hi Steve,
On the first set of engine plates for K1....there is a reason that i had a new set cut....careful marking out of the 4 outer most holes in one plate & drilling all 4, adding a roll pin in each as i went held them while all the others were drilled. 4 plates 5 mm thick & LOTS of 3 mm holes latter, 20mm roll pins were just the ticket, easyish to knock out so swarf & de-burring etc could be done with the hopeful knowledge that i could get them back together & carry on!

Cheers Kerrin

[racinjason]

They are a great and simple to use but I have had one start to collapse and let the assembly move out of alinement but to be fair the parting line was 90 degrees to the rotation so this probably contributed to the failure. I'm not a fan of the look of taper pins but I do use them.
cheers Jason

[SteveW]

Yep. A vote for as being simple, cheap and maybe dirty but a whole lot less faff than taper pins.

No point to being precious about using or NOT using the things.

What's not to like?

[mbrown]

The great advantage of taper pins over roll pins is when you need to remove a pin easily. A taper pin comes free with just a tap on the small end but a roll pin has to be driven out with a drift which is not always feasible.

I use quite a lot of 1/16" taper pins for jobs like holding a handle onto a spindle. I use small roll pins (3/64" or 1/16") for similar jobs which are meant to be permanent but which might need dismantling very occasionally and where a suitable drift can be applied to the end of the pin.

Horses for courses, in my opinion.

Malcolm

[doubletop]

Martin Evans suggests roll pins as one of the methods of assembling the Dart crank. The builder of my Dart had done just that and over time the crank webs had come loose. It could well have been the tolerances the builder had used for the webs, axles and bearing journals. However, I assumed that the constant variable loads on the roll pins had caused them to collapse slightly and the joints failed.



I used solid pins in the new crank I made to replace it but they weren't sucessful and failed after about 5 years.



For the latest variant I used taper pins.

Pete

[ettingtonliam]

I suspect from your videos that the root cause of the problem in the earlier versions was the poor fit of the individual crank axle components. No pin, be it roll, solid or taper, is going to overcome that.

[doubletop]

Jun 26, 2022 7:14:17 GMT ettingtonliam said:

I suspect from your videos that the root cause of the problem in the earlier versions was the poor fit of the individual crank axle components. No pin, be it roll, solid or taper, is going to overcome that.

I agree. But when you are doing these things for the first time, without the benefit of years of experience that some may have, you look at the problem and try to reduce the risk of it happening again.

My attempt of using stainless solid pins in reamed holes also failed aftre 5 years. That despite spending ages getting the holes in the webs as accurate as I possibly could.

The third version, my second, I used taper pins as well as 'cotton reeling' the axle and journal pins. A method that had been advised by others. The holes on the webs were reamed, rather than only relying on accurate boring and then the axle and journal end turned to size. (I think the reamer cost me more than the material to make the crank). In both cases I used high temp, high strength loctite 620.

It remains to be seen if it lasts.

Pete

[Gary L]

Jun 25, 2022 12:33:21 GMT mbrown said:

The great advantage of taper pins over roll pins is when you need to remove a pin easily. A taper pin comes free with just a tap on the small end but a roll pin has to be driven out with a drift which is not always feasible.

I use quite a lot of 1/16" taper pins for jobs like holding a handle onto a spindle. I use small roll pins (3/64" or 1/16") for similar jobs which are meant to be permanent but which might need dismantling very occasionally and where a suitable drift can be applied to the end of the pin.

Horses for courses, in my opinion.

Malcolm

…which raises the next question… how to get a really good fit with a taper pin reamer; not too big, not too small, and without the reamer jamming and breaking. Trial and error and gentle bites gets there in the end, but is there a ‘right way’ -? Roll pins lend themselves much better to ‘mass production’ but I agree a taper pin is a better job.

Gary

[mbrown]

My 1/16" taper pin reamer has served me for decades and I have never broken one. I have even used it under power in the pillar drill, which is probably appalling practice but worked... I always use a cutting paste like Trefolex and clean the flutes at intervals as the cut progresses.

If you start with a fairly long taper pin, the exact size of the hole is not too critical - tap the pin home tightly and trim off the ends. The trimmed bits can often be used in other locations. My 1/16" taper reamer is long enough to work for pins bought as 5/64" taper pins too, and I have a 3/32" taper reamer which picks up at the top end of the range so any size pin is catered for.

I usually start by drilling a hole which allows the tip of the reamer to enter by 1/8" or so, then open it out until the reamer is cutting for the full length of the hole.

Incidentally, there are locations on full size locos, such as coupling rod retaining collars, where taper pins were often used and it is easy enough to folliw suit in our sizes.

Malcolm

[Deleted]

To add to Malcom's words, I also have had no issues with 1/16 taper pins and often use them under power if happy with the setup, some situations I resort to hand power to feel my way.
Regarding roll pins, I'm not a fan as have seen them fail. Having said that this could be down to poor fitting but personally I prefer a solid pin.
My experience with failed roll pins is down to the part built Heilan Lassie that I rebuilt. The crank failed due to this type of pin being used, the builder had used these throughout the build, crank, wheels and some motion parts. IIRC one of the crank wheels also failed after a few laps of the club track. When you consider the torque that is exerted on the crank and wheel to axles it's probably asking too much when using a hollow pin. I don't recall any of the roll pins used for the motion failing although to be fair the model hasn't seen much track action. As stated this could, of course, be down to poor fitting originally?

Pete

[SteveW]

Guys,

One point and one question:

Maybe worth considering a roll pin as a safety feature. Agreed, a total pain when they go but it can sometimes save a lot of bent metal.

Last time I used taper pins, at school, they followed a taper drill. Not sure I've seen these for a while. Have I been looking in the wrong places or what?

[flyingfox]

Greetings, I prefer taper pins myself, mainly because I have had trouble getting them out.
I understand that metric and imperial taper pins have a different taper, if so mixing them in error may give unreliable fits.
Regards
Brian B

[Deleted]

Jun 26, 2022 16:18:19 GMT flyingfox said:

Greetings, I prefer taper pins myself, mainly because I have had trouble getting them out.
I understand that metric and imperial taper pins have a different taper, if so mixing them in error may give unreliable fits.
Regards
Brian B

IIRC Brian one has a taper of 0.48 while the other is 0.50...I believe that the imperial pin is 0.48 but won't swear to it.. when I drill for taper pins I use a slightly larger size drill than the smallest diameter of the pin so that I can get a reasonable length of the reamer into the hole before cutting. . I then use the reamer and stop when the pin sits roughly in the middle.
As you guys will know taper pins are available in different lengths, I prefer to use the longer pins which seem to go down to a slightly smaller tip.

Pete

[doubletop]

I've never had a problem with taper reamers, I've used 1/16" taper pins and, I believe, they were 3/16" for my crank. I start with a hole that is the size I want the thin end of the pin to end up being. I put a stop on the reamer so all the pins end up being the same dimension. For the larger sizes I've reamed under power, plenty of Rocol to help with the lubrication and remove frequently to clean off the swarf. It isn't going fall out of the small hole at the bottom.

Pete

[jma1009]

As I seem to have started this off on Steve's O2 Calbourne thread, I am happy for the Moderators to transfer my post to here.

I ought also to edit the above because Stepney's crank axle is press fitted and with taper pins, and like Malcolm and others I had quite forgotten I'd done it this way.

The major problem is a crank axle with 4 eccentrics for Stephensons valve gear.

I've never had an issue with reaming with a taper reamer. Never done it under power and always by hand. I must have 3 or 4 for the small sizes including one with spiral flutes. Rocol cutting compound. I also have a set of large taper reamers going up to 1/2".

As mentioned on Steve's other thread I have an intense dislike of roll pins.

[simon6200]

A friend advised against taper pins saying they often are impossible to remove. I recently tried to remove a lifting arm from the weighshaft which had been pinned with a 2 mm roll pin. Somehow the roll pin was bent in the joint so it is impossible to remove the lifting arm without cutting it away and making a new arm. I worked around having to remove the arm but I won’t be using roll pins again. My friend can be a bit of a bodger so might not have fitted the taper pins properly. I imagine the trick to removal would be to ensure you don’t mushroom the small end.

[springcrocus]

Well, this thread has generated a fair bit of interest and there seems to be a general consensus that roll pins are usually to be avoided. Julian was right to question my use of roll pins for locking the crank webs to the journals but, in my defense, the crank axle should never need to be disassembled and the joints were all a firm press-fit to start with and may not even have needed pinning. The holes in the webs were reamed with a 14mm reamer and a plug gauge made that just started to go in the hole. This was measured with a micrometer and all journals subsequently turned two thou larger than the plug gauge. That's how I tend to make press-fit items, anyway.

I do question the use of taper pins in preference to roll pins where long distances are involved but, as a machinist, I tend to automatically "machine" everything rather than do it by hand so am at greater risk of breaking things.

My personal feeling is that if it may need dismantling, use a taper pin and if it's fixed for life, use a roll pin. I seldom use solid pins as it requires a reamed hole and, unless the pins are silver steel, are often slightly undersize.

Saying all that, no amount of pinning is going to fix a poorly-made joint. A sloppy joint is always going to fail at some point along the road. Get the joint correct and the pin is just an additional safety measure.

Regards, Steve

[Deleted]

Hi Steve

Just to clarify my view, I wouldn't use a taper pin for the crank either. Taper pins are for parts that need disassembly, as you rightly say once built a crank should be permanent.
Keep up the great work, the model looks great.

Kind regards

Pete

[ettingtonliam]

Just to be difficult, I don't like built up cranks anyway. Yes I know that for a loco with eccentrics there isn't much option (although one or 2 intrepid souls have machined one from the solid), but for single or double throw cranks for stationary engines I've always machined from the solid. Several of them were quite large, 1 1/8" journals, 4" stroke for a gas engine. I used flame cut blanks of Grade 50 structural steel plate, because I had a friend who managed a fabrication and he arranged them for me.