Butterfly Bolt or Thumb Screw

Hi,

I am in the process of converting my scroll saw and the blade holders currently are M4 cap headed socket screws marked 8.8 which is I think high tensile alloy steel.

It would be an advantage to replace the cap headed screws with finger tightening screws such as thumb or butterfly.

My issue is that yes I can find stainless screws to my requirements but not strong steel. Easy to find cap headed screws so is there a way to convert a normal cap headed to convert to thumb or even better butterfly.

I have found one site offering really strong durable M4 butterfly bolts but i suspect I could fall foul of certain shortcomings from our overseas manufacturers in terms of quality.

Any suggestions welcome

Chris

Saw a slot across a cap head screw, saw/file up a pleasing shaped head from steel sheet and silver solder into the slot

another option is to take some steel bar, turn down and thread one end to the size you need and then saw off leaving sufficient to form a head. How hold by thread and turn the hean to an oval or round shape. mill the two sides flat and you have a thumb screw

Edited By JasonB on 05/07/2020 16:37:52

Chris

so you want to convert a blade locking screw that you use an allen key for to a finger lock?

use a m4 bolt as the post and use a m4 wing nut on it to use as the lock...if the wing nut or bolt wears out ...replace it...?

I would suggest you make a key. Retain the cap heads and make a key similar to a clock key with a suitable sized piece of hex from a cut down allen key driven into the pipe. Create a suitable holder on the saw for the key. A block with a hole in would be the simplest. You can make the key as wide as you like for ease and as long as you like for access.

regards Martin

Edited By Martin Kyte on 05/07/2020 16:43:03

Thanks Guys,

The M4 bolt is basically pinching together a piece of steel with the far end threaded. Would a simple and effective solution also be to do what Ian states adding a butterfly nut to the steel bolt but use a strong loctite that stays in place such as retaining compound 680?

Chris

Edited By Chris TickTock on 05/07/2020 16:44:29

Like it Martin, something I had not yet thought of.

Chris

Cross drill the head of the cap screws and drive a small roll pin through it to make a handle. You can put a larger roll pin over either end of the original roll pin in order to make the handle a little larger.

Martin

Chris

just run a m4 bolt into the thread after putting a wing nut on the bolt

then use the wing nut to tighten it up

the nut does the same job as the bolt head

Whatever mods you do strength of the screw won't really come into it as your finger and thumb will never apply as much force as an allen key would unless you are built like Popeye.

Just buying a Tee headed allen key would be another option and give the same effect as Martin's suggestion.

The thing about my suggestion is that you dont wear out the female thread in your equipment

the bolt shaft is replaceable when it wears out as is the wing nut

Yes and this is probably the most pragmatic. Can I get M4 butterflies in strong steel? For this type of application is carbon steel essential?

Chris

Chris

if it lasts even 6 months replace the screw or the nut a bag of 10 wing nuts will last a lifetime...guaranteed

As I said above you will be hard pushed to strip an M4 wing nut using finder and thumb, if you are going to tighten it with pliers then maybe in which case whey change from allen key

I have just looked up the tensile and yield strength of A4-80 stainless v 88 steel and surprisingly not a heap of difference. I note it is easy to find more steel components in the states...we should support our steel industry but I had better watch it I'm becoming political. Thanks Guys..problem sorted.

Chris

You can get moulded cps specfically to turn cap screws into "knobs"

https://uk.rs-online.com/web/p/knobs/0771667/

Other suppliers do them too.

Robert G8RPI.

< deleted as irrelevant >
 

MichaelG.

Edited By Michael Gilligan on 06/07/2020 08:25:45

Thanks for the link. The economically-minded can easily make them, of course, and brass seems convenient for its relative softness.

Nothing wrong with being patriotic but never ignore uncomfortable realities! One is that Brits would have to buy an enormous amount of steel to make a difference.

In 2019, the UK made 7,200,000 metric tons of steel, about a million tons more than Holland, and slightly less than Egypt. At 87.9MT the USA was the fourth largest producer of steel in 2019 after Japan (99.3MT), India (111.2MT), and China who made a whopping 996.3 million tons, about half the worlds' steel (1869.9M) To put that in context, China made more steel in the last 3 years than the entire UK steel industry since the industrial revolution.

Bringing British Steel up to Chinese levels would need every man, woman and child in the UK to buy about 16 tons each year forever, and they'd have to buy it whatever the cost. Producing that quantity of steel in the UK would require massive investment of money and land in steelworks, and seaports. It would very difficult to mass produce steel competitively because today most of the Iron Ore, Scrap and Coal has to be imported. Not much coal or iron ore left underground in the UK.

Patriotism isn't the reason more steel products are available in the USA. It's simply there's a bigger market for them, partly 330Million people vs 67M, partly because of what they manufacture. In general, big markets result in more choice and lower costs, and the USA is big.

British steel is unattractive to model makers for another reason. Like many other steel producing countries, Britain has shifted away from mass production of cheap carbon-steels into making high-quality alloy steels for specialised purposes. One example is railway lines where the steel must be strong, reliable, weldable and extremely wear resistant. Likewise special steels for lightweight bridges, pressure and corrosion resistant chemical plant, turbines, oil rigs and other highly demanding applications. These steels are expensive, high-quality and mostly useless in a home workshop.

Supporting local industry and services may be good politics but always check the reality - emotional decisions are often expensive mistakes. I'm divorced!

Dave

Informative stuff Dave, thanks for the post.

Chris

Using a suitably long bolt, thread a butterfly nut onto the end until just fully engaged, silver solder in position, then cut off the head. I've used that process to make metric hex-head bolts in various sizes not available commercially. For most model engineering uses you will strip the thread before you break the silver solder bond.