Machine v Self-Tapping Screws

[Ian_Rob]

To avoid any chance of the exposed thread chafing halyards within an aluminium mast, I have been advised to use machine screws rather than self-tappers. I don't quite understand. Will it be necessary to drill and then thread each holes or what?

 

[David2452]

Either that or use ali rivnuts.

 

[alahol2]

To use machine screws, yes you would need to tap the hole. I have successfully used a machine screw to 'self-tap' but it can be a fiddle and may not work. Personally I use monel rivets for fitting anything to my mast.

 

[David2452]

yes you would need to tap the hole.

Not if you use rivnuts.

 

[Ian_Rob]

Not if you use rivnuts.

Thanks for the replies. It is track to take a sliding pole car. Will rivets work ? ie can they in effect be countersunk?

 

[David2452]

Thanks for the replies. It is track to take a sliding pole car. Will rivets work ? ie can they in effect be countersunk?

Yes, you can get countersunk rivnuts in a range of threads, I use them in lots of "blind" situations instead of pop rivets as then the job is easily dismountable if it needs service or replacement. See here for just one supplier, http://www.namrick.co.uk/acatalog/Aluminium_CSK_Head_Rivet_Nuts.html
The right install tool makes things easier but for low volume a bolt and nut can be used to install them, just a bit more time consuming.

 

[Ian_Rob]

Brilliant. That's great. THANKYOU

 

[DaveS]

The right install tool makes things easier but for low volume a bolt and nut can be used to install them, just a bit more time consuming.

I'm trying to visualise how that would work if you don't have access to the other side.

 

[David2452]

I'm trying to visualise how that would work if you don't have access to the other side.

You hold the bold head still with a spanner or allen key and tighten the nut against the rivnut, a washer and a bit of oil helps, a bit like using a puller.

 

[DaveS]

You hold the bold head still with a spanner or allen key and tighten the nut against the rivnut, a washer and a bit of oil helps, a bit like using a puller.

Ah, I understand - with you now.

 

[David2452]

Ah, I understand - with you now.

It's the principle that the nice newer setting tools use instead of the old pop rivet type pliers that used to bend easily.

 

[Ian_Rob]

Probably a naive question but as it's blind, how do you know you have given it sufficient turns? Too few or too many seems to be an issue??

 

[David2452]

Probably a naive question but as it's blind, how do you know you have given it sufficient turns? Too few or too many seems to be an issue??

Without the tool its really a "feel" thing, but its really difficult to get them too tight, practise on a bit of ali sheet to get the feel. Worth the trouble because apart from this job they are really useful in many other areas, boaty and non boaty, at least I find it so.

 

[Ian_Rob]

Thanks David I'll try them.

 

[KevinT1]

David,

do the Aluminium Rivnuts you linked to ( Namrick ) have a stainless nut in them or a mild steel ? and is the body aluminium ( the part that deforms ) ?

I guess the Stainless Steel ones that they list are all stainless - is that correct ?

What are your thoughts on the Silverline tool that you can get for around £15 - similar to a Pop rivet gun - I ask because my experience of Siverline tools is not that good

Thanks

 

[William_H]

I can't imagine why people on this forum seem to be afraid of drilling and tapping a hole. I use 3/16 and 1/4 inch ww taps a lot on my little boat. Metric the same if they are the bolts you have available. Especially in Ali a tap is a doddle. You can use a slow speed battery drill with the tap in the chuck. Whizz it in then reverse out. Use duralac on the screw before you put it in.
Taps are really quite cheap just buy the standard first tap.
Yes a machine screw can be the precise length to suit the mast wall thickness wheras a self tapper will always have a poiny end sticking into the path of halyards. good luck olewill

 

[Ian_Rob]

I've only tapped a few times and only by hand. Isn't there a risk of cross-threading the tap if I use a power drill - even at slow speed? I will be doing the uppermost fixings whilst dangling in a bosuns's chair, so I would like to use the method that is going to be the easiest and most precise.

I'm not sure how much purchase is going needed to fix a Rivnut - presumably not that much into aluminium - but if effort is required , threading might be the easier option?? There is 4.2 m of track with fixings at 100 mm centres.

 

[David2452]

David,

do the Aluminium Rivnuts you linked to ( Namrick ) have a stainless nut in them or a mild steel ? and is the body aluminium ( the part that deforms ) ?

I guess the Stainless Steel ones that they list are all stainless - is that correct ?

What are your thoughts on the Silverline tool that you can get for around £15 - similar to a Pop rivet gun - I ask because my experience of Siverline tools is not that good

Thanks

All rivnuts I have used are entirely made of the material specified i.e. brass, Ali, Mild steel, stainless, the only exeption I have come across are the rubber ones used to mount stuff needing electrical insulation or as vibration transmission barrier, but they are not technivcally rivnuts anyway. As has been said, tapping is easy... but.....usising rivnuts gives you more threads engaged than tapping in thin materials and are easily replacable with the same size if the thread becomes damaged, the prime reasons for using them. I have some experience of the pop rivet type of aplicators as I mentioned earlier in the thread, a cheap one may well last long enough to use a few soft Ali inserts or even longer, £15 isn't much to find out as if it is not fit for purpouse then you can return it if a retail buyer. My heavy one is more like a pair of bolt croppers and I have a Defra cordless one for when I have a lot to do. It is very important to use the correct bit size for the right results, close enough is not good enough, don't ask me how I know.

 

[30boat]

I've only tapped a few times and only by hand. Isn't there a risk of cross-threading the tap if I use a power drill - even at slow speed? I will be doing the uppermost fixings whilst dangling in a bosuns's chair, so I would like to use the method that is going to be the easiest and most precise.

I'm not sure how much purchase is going needed to fix a Rivnut - presumably not that much into aluminium - but if effort is required , threading might be the easier option?? There is 4.2 m of track with fixings at 100 mm centres.

Always tap by hand.Using a drill is not the way to go.You need to feel the tap cutting and will need to back it to clear the swarf.

 

[trapezeartist]

Always tap by hand.Using a drill is not the way to go.You need to feel the tap cutting and will need to back it to clear the swarf.

Agreed, but you can also use self-tapping screws. First remember that the screw will be rolling the thread, not cutting it, so drill an appropriately bigger hole. Run the screw in to make the thread. Then remove the screw and grind off the point so that the screw is only as long as the combined thickness of the fitting and the mast wall. Then refit.