fed up with unc

[alacant]

Hi everyone. I can walk into any hardware store and get m5 -or mwhatever- bolts off the shelf. Each time I need an 1/4 unc, it's a 2 week wait from ebay. 

1. Can I send just send a m5 tap through a 1/4 unc hole and expect it to hold?

2. Is it possible to use a hand held power tool to drill a 4mm hole in a vixen dovetail or must I go to a machine shop?

Cheers.

[happy-kat]

There is a fantastic little shop in Hove that have lots of stuff in unc imperial metric you name it and they do mail order if you can't walk in.

[ChrisLX200]

1: Nope, 6mm is your closest and even that's a little undersize. There won't be much metal left after putting a 6mm tap through a 1/4" UNC threaded hole.

2: Yes, simple job.

ChrisH

[alacant]

Thanks. Why are the dovetail holes threaded anyway? Is there anything wrong with going m6 nut and bolt rather than unc bolt only? I just want to put a clamp on a piggy-back dovetail: TIA

 

[Peter Drew]

Whitworth thread standard follows UNC on TPI up to 1/2" where there is 0ne TPI difference. Whitworth is 55 degree thread angle opposed to 60 degree for UNC so Whitworth threaded screws will usually fit UNC but not vice versa.    

[Scott]

I've drilled plenty of holes in dovetail bars. just drill a 2mm pilot hole first :).

[Davey-T]

Just drill and tap a couple of 6mm holes to suit.

Dave

[alacant]

 

Just now, Davey-T said:

drill and tap

Ah, the tap again. Why not a hole with a nut and bolt? There must be a reason because every dovetail I've ever seen has threads!

[Davey-T]

1 minute ago, alacant said:

 

Ah, the tap again. Why not a hole with a nut and bolt? There must be a reason because every dovetail I've ever seen has threads!

A nut could foul something and a hole is cheaper than a nut 

Dave

[alacant]

LOL. OK, I'm convinced. I'll put the cost of the nut towards my next takahashi!

[Davey-T]

Just now, alacant said:

LOL. OK, I'm convinced. I'll put the cost of the nut towards my next takahashi!

Someone like Sky Watcher supplying thousands of dovetails would save the cost of thousands of nuts 

Dave

[Thalestris24]

A bolt and (locking) nut would be fine so long as it doesn't cause a problem underneath the dovetail. If necessary, you could be clever and countersink the dovetail so that a countersunk-type bolthead lies flat underneath 

Louise

 

[Peter Drew]

Having a nut protruding at the ends of a dovetail could prevent the scope slipping off the mount.  

[Alien 13]

18 minutes ago, Peter Drew said:

Having a nut protruding at the ends of a dovetail could prevent the scope slipping off the mount.  

It does 

Alan

[alacant]

9 hours ago, Davey-T said:

Sky Watcher supplying thousands of dovetails would save the cost of thousands of nuts

They can't be that far off ordering their Tak by now then!

[glowjet]

Instead of hardware shops, try some local garages or machine/fabrication shops, you may be lucky, some may have 1/4" Whit or 1/4" UNC in their spares box.

Won`t any of the Ebay sellers, by arrangement, be prepared to send by special post to Alicante ? two weeks seems an awful long time to wait for post

[Davey-T]

I usually use these guys , really fast efficient service, generally arrive next day, they send to foreign parts and even answer the phone 

Dave

http://www.a2stainless.co.uk/

[alacant]

OK. I chickened out of the tap I'm afraid, but the bolts worked OK. One spin off I didn't expect is the rigidity the second dovetail along the top of the rings gives. Thanks everyone for your encouragement.