Hole Wizard Help Needed

can someone explain to me how hole sizing works in the hole wizard on solidwork? I used a vernier today to measure a counter bore screw. It gave me 7.8mm but I cannot get this on the size type on the hole wizard, a M6 is too small and an M8 is too big! can someone please explain to me how it works

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4 Answers

There are no "counter bore screws". Screws are defined by their features such as head type, length, material, thread...etc. Counter bore is a type of hole like a counter sink.

Screws are given nominal dimensions. The 7.8mm screw you measure is most likely an M8.

Holes made for a screw need to have clearance. Basic clearances can be defined in the Hole Wizard as "normal, close, or loose". Or, you can specify a clearance, but I hope you use a standard sized drill bit. No machinist wants to bore a ream a custom sized hole for a bolt to slide through.

Without clearance, the bolt will not fit in the hole.

 
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The easiest way to identify a thread on a bolt is to fit it with a nut of a known size.

If no nut is available, then you should have a thread measuring gage. They are pretty simple, but it will determine the pitch of the thread.
Metric threads use pitch. Imperial threads use threads per inch. One divided by threads per inch (tpi) = pitch

Then you will need to measure the diameter (as you have done with calipers).

The last step is consulting a chart for common metric and imperial sizes.

7.8mm should be an M8. M8 bolts will have a pitch of 1.25 (standard), or 1.0 (fine). If the thread gage gives a different reading, then you could be reading it wrong, you’ve got a non-standard bolt, It could be a really old bolt, or it could be an imperial bolt. Some of the metric and “standard” sizes are really quite close and difficult to identify by eye alone.

7.8mm is really close to a 18 gauge bolt, but 18 gauge is a really uncommon size. 5/16 would be a more common size to confuse with an M8.

5/16 bolts come in either 18 or 24 threads per inch. Those are pitches of .05 or .04, so using the thread gage can really help to narrow the size down when the diameters are close.

 
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Hi Fred,
Sorry I've been offline a while. See the attached file is a drawing of a sensor. If I was design it up on solidworks (make a copy of it) how would I design the M18 x 1 part? do you just draw a circle and extrude it 5.5mm and put on a cosmetic thread of M18 x 1 to get the threads or do I have to do a swept cut? Also if I was looking to make a threaded cap for it how mould I do it? would I just make a cap at 20mm and then put in a M18 hole?

This is what I find hard to understand

 
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Seona,
A lot will depend on how accurate the model has to be.
To design the boss for the M18 thread, I’d go to a site like this: http://mdmetric.com/tech/M-thead%20600.htm Or, look in the tables provided in a copy of the Machinery’s Handbook.
In both locations you’ll get a range of diameters which are acceptable for an M18x1 thread of a certain tolerance class. In this case, the Outside Diameter for the thread needs to fall between 17.79mm and 17.97mm

How you create this in your model really depends on how the part will be made, and if you need to show the threads for any reason. That is what the image you are working from shows, no helical thread was added to the drawing.

The simplest option is to simply extrude a boss with a diameter of 18mm and allow the people making it to do the rest. For standard threads, there are not many reasons to draw them in the CAD model. Drawing threads is time consuming, and it makes the file much larger in size.

I’d say the three best arguments for modeling a thread are:
1- You plan to 3D print the part and it needs to have a thread.
2- You plan to make a nice rendering
3- You are making a drawing, and want to show the threads
If you are not doing one of those, then just use a thread callout.

A threaded cap works the same way, but the diameters and tolerances of an internal thread are different from external threads

 
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