Knob not tightening right

  • #1
tirelessphoenix
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TL;DR Summary
help with knob screws
hi, I am having an issue with a knob-like screw. the original screw, seen in figure 1 A tigthens the hole in the figure 2 very good, but I tried to replace it with a knob like the one in Figure 1B, but it does not tighten right. both are an M6 type. I tried similar knobs like Figure 1B in sizes M5, M4 but are too thin. Does anyone know why Figure 1A screw tightens good but not the one shown in Figure1B? even both appear to be from same size and get into the whole ok?
Does anyone know if a knob of M6 size with a pointy ending like shown in Figure 3 exists? I don't know how to search it...what name to use...
thank you
TP
Figure.jpg
 
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  • #2
tirelessphoenix said:
TL;DR Summary: help with knob screws

Does anyone know if a knob of M6 size with a pointy ending like shown in Figure 3 exists?
There is no special name, and the knobs are not commonly available with special ends. You will need to grind a point onto the end of the thread.

The knobs tend to have a poorly formed thread at the end. They have a hollow in the end because the thread is rolled, not cut. That makes the thread easy to start, but a sloppy fit. Grind, or cut off, maybe the five end threads, then grind or file a shallow point or ball onto the end.
 
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  • #3
I understand. Which machine does the grinding best?
 
  • #4
Angle grinder?
 
  • #5
Take care while grinding the thread, if holding the knob by hand.

If you only need to grind one, use a grindstone or a linishing machine.
Another possibility would be an angle grinder, or a Dremel tool.

If you do not have the tools, find a local car mechanic who should be able to do the job quickly.

A hand held file would do the job if it was all you had.
 
  • #7
Yes, but a Dremel tool would be more use and less cost for other small jobs.

You might attach the knob to a solid structure before using the grinder, or attach the grinder before holding and controlling the knob by hand.
 
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  • #8
ok
 
  • #9
tirelessphoenix said:
the original screw, seen in figure 1 A tigthens the hole in the figure 2 very good, but I tried to replace it with a knob like the one in Figure 1B, but it does not tighten right. both are an M6 type.
Could be possible that the original screw is 1/4"-28 crests per inch rather than M6-1.0 mm?
 
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  • #10
Lnewqban said:
Could be possible that the original screw is 1/4"-28 crests per inch rather than M6-1.0 mm?
Here is how to tell.

Hold onto the knobs, hold the original in one hand and the replacement in the other.
Bring them together side by side so the full length of the threads of one mesh with the threads of the other one.

If the threads do not mesh perfectly uniform over their full length, then they are different threads.

The other possibility is that the item with the female thread is damaged and the original threaded knob is worn enough to mostly work.

Cheers,
Tom

p.s. Differing male+female threads often mate 1/8 to 1 turn then stop, that is another clue.
 
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  • #11
tirelessphoenix said:
I understand. Which machine does the grinding best?
Filer/sandpaper and electric drill/screwdriver. Fix your knob into the drill and set it to (very) low speed.
Put a nut on the knob first, so you can fix the thread just by removing it.

Baluncore said:
The knobs tend to have a poorly formed thread at the end.
Also, that plastic 'knob' part just makes it convenient to be used by hand, but usually not really helpful with torque and precision.
 
  • #12
Grinding small screws:

FH17ONO_582_07_029.jpg
 
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  • #13
perfect
 
  • #14
jack action said:
Grinding small screws:
I think the point needs to be precisely centered for this role.
 
  • #15
What does "precisely" mean quantitatively? How good is your handiwork? If you can rotate the piece while grinding this can be quite precise.... or touch it up at the finish somehow by rotation.
 
  • #16
Rive said:
I think the point needs to be precisely centered for this role.
My bench grinder has a guide for grinding drill bits. You can see it in the image from my previous post, but you see it better in this next image.

It might be more difficult to use with a short screw - especially with a large head - but I'm sure a resourceful person will manage to find a way to make it work.

fb5bfbfc80fa7cf61d7f4c44e6e7b3b1.jpg
 
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  • #17
Rive said:
I think the point needs to be precisely centered for this role.
You can chuck it into a drill and turn it while against the grind stone. Thread a nut on to improve the grip.
 
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  • #18
tirelessphoenix said:
TL;DR Summary: help with knob screws

but it does not tighten right. both are an M6 type.
Are you sure that the pitch of the threads is the same / appropriate for the thread in the hole? (Sorry, this has been said already but it could be highly relevant!)

If you want to make sure of threads matching (or just cleaning up) then why not get hold of the right size and pitch die and tap (Cheap versions will do).

Why not contact the manufacturer and find out the actual thread dimensions. Are you absolutely sure that the thread is metric? There are many other alternatives (especially in US) and some threads are still used for specialist purposes. Do some homework before further machining effort.
 
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