# Screw threads and bearings (how to )

1. Aug 21, 2007

### Andreii

Hi everyone
I am trying to learn how do I correctly draw, with a ruler (where are milimeters visible as much as possible) and pencil, on already given surface screw thread and on another surface (different task) how do I correctly draw, lets say, pair (or it can be just one too - study of drawing in this case is prolly the same) of (ball) bearings.
Unfortunately I don't have an example of ''putting'' bearings on given surface but I am showing taskes, which we have done on university, how to draw screw thread on surface. From this, it might be obvious what I would like to do with ball bearing.
To begin with, I am showing ''empty'' surfaces with different color HERE. As you can see on the link there are actually two the same taskes. Green color (given surface) and blue color (definited locations) shows what is given in the task, everything else (lets overlook the points which are given by teacher) is student's work.
This screw thread contains bolt M10x40. The colors might be a bit annoying, so I am showing again, without colors HERE2.
The upper picture is work of my mate who used to lend me the task. He got 50 points out of 50. The other picture, at the bottom, is my work. I got only 5 points out of 50. I won't ask how to draw this but is there any tutorial how to correctly draw screw thread as that one (Mzzxzz where ''z'' is the number) and also how to put on the surface ball bearings as I used to put the screw thread here?
Another example, which we had on exam is THIS. Here is bolt M12 with length 55mm and screw (?) 36mm (36 is inside those 55mm of course). Surface is given, definited locations, which shouldn't be really necessary here, are also given. Everything else is my work. I got 4 points out of 20 on exam in this task. I know, I made big mistake in the ''head'' of the bolt already. If you look at it, a part of ''head'' is into surface and it should be outside. However, im afraid this is the only thing I know what I did wrong. Red colors shows teacher's correction - it could be obvious.

So, I would also like to please if someone could check what I have learned so far - here are the following statements that I described while studying. I know the following statements aren't enough to draw the whole screw thread, thats why I asked for tutorial also. The only thing I would like to please in those statements, are to correct me if I am wrong. For better view at the task, I made ''additional zoom'' on the picture, so more details will be visible. Here it is: CLICK2

1. We usually begin with bigger size of screw - I could name that ''outside size'' also. Since bolt is M10x40, the length between Location 1 and Location 2 must be exsactly 10 mm.
But is to which location do both lines go definited too? In the task could be a trick - part of surface (where location 1 and 2 end) wouldn't be there.

2. As I mentoined in the task we have the bolt M10x40. So the length between Location 3 and Location 4 is exsactly 40 mm.

3. I also study from THAT book. From it, I have seen an information that we can get the length between Location 3 and Location 5, on the following way: We know we have 40mm length (my previouns statement). From the tables I see the length from Location 5 and Location 4: 40 - 4.5 = 35.5 and because of this is 40 - 35.5 = 4.5 mm, so the length between Location 3 and Location 5 is 4.5 mm. This is the way which this book shows but on the drawing I really doubt if this is 4.5 mm.
Keep in mind that I haven't really mentoined those tables in my post or locations on the network to see them. I have them near my hand thats why. If someone would like to take a look at my tables, please let me know and I will put them here for you.

4. Because of this type of the bolt (M10) the ''inside size'' (between Location 8 and Location 9) is exsactly 8.3 mm. If I look at the drawing, it answers exsactly this

5. Length between Location 4 and Location 7 is 7.3 mm.
Here I am a bit in doubts. Is it really from Location 4 to Location 7 or is it from L. 6 to L. 7? Table and the book (not the one which I showed, I study from several books) shows from L. 4 but if so, I have absolutelly no idea what to do between L. 4 and L.6 - there might be also specific angle that we have to remember but, as we see at the end of screw thread, it isn't the only angle that is important.

6. Length between Location 3 and Location 10 is 7 mm.
But how do we divide that?

There are more other subjects that are important here but I still haven't figured them out yet. However, Im not sure what to do with ball bearings if I try to draw them like that. I haven't found explanation of this anywhere yet. While searching for explanation for screw threads, I haven't had much luck. Many sites show me something similar to THIS3 but it isn't really so useful for my opinion.
Engineering standards that I used (just for screw threads) are:
SIST ISO 724 / DIN 13
SIST ISO 6410 / DIN ISO 6410 / SIST ISO 3508 / SIST ISO 4755 / DIN 76
SIST ISO 24032

Thank you for any kind of help.

2. Aug 21, 2007

### Danger

I hate to say this, Andreii, but I'm finding it almost impossible to determine exactly what it is that you want to do. We have a really serious language gap here, although you're doing very well if English isn't your native tongue.
The closest that I can figure out is that you want to overlay draughting symbols on a pre-existing 'blank' outline. Is that it—to 'fill in the blanks' with the proper symbols?

3. Aug 22, 2007

### Andreii

I would rather not call this '' draughting symbols '' but yes, I want to draw on '' pre-existing 'blank' outline '', which I named ''surface'', screw thread and on another ''surface'' (of course different one because its totally different task) ball bearing.
Some mates on university told me its so easy to draw the ball bearing on surface but when the teacher showed us correct task about ''drawing a ball bearing on surface'' and wrong one, I saw almost no difference which means there can be million of mistakes.
I haven't had any task at home for ball bearings, so I just showed for screw thread.

4. Aug 22, 2007

### FredGarvin

I am too having troubles with what you are asking, so forgive me if I overlook something. What I think you are asking is 1) How do you properly detail a drawing for a threaded fastener and 2)How do you graphically show a bearing?

Before getting into this, I can not understate the importance of getting a copy of Machinery's Handbook. It is a MUST HAVE for anyone in the design field.

1) You are on the right track with what you are doing with the bolt drawing. First though, there is some terminology that should be addressed. In the hole location for the bolt, the first step that is usually done is to drill the hole with the "tap drill." The tap drill is an undersized drill that establishes the minor diameter of the threads. In my chart for an M10, I have listed an 8.5 where you list an 8.3. They are both fine. In your case this simply means that there will be slightly more thread engagement because of the smaller diameter. You do want to be careful with tap drill selection because one that is too small becomes very difficult to tap for the machinist. Usually a 75% thread engagement is plenty. Since you stick to ISO threads, the way to calculate the proper tap hole diameter is:

$$DIA = B- ((1.08253)(P)(F))$$
Where
DIA = Tap hole size
B = Basic Major Diameter of the thread form
F = Percent of Full Thread (engagement)
P = Pitch

The distance you drill the tap drill is the tap drill depth. That will always be longer than your thread depth. This extra depth allows a place for chips to go during the thread tapping process. There are many rules of thumb that people use to govern how much deeper to go. Essentially you need to provide, at the bare minimum, enough extra depth to allow for the chamfered end of the tap to protrude through the threaded portion of the hole. This will ensure that you have complete threads the entire depth.

2) Bearings could be an entire class in themselves. There are many types of bearings and their configurations can change depending on their usage and the desired audience of the drawing. Drawing a bearing can be very simple, like this: http://www.engineersedge.com/bearing/images/ball_bearing_tolerance.gif
This is a simple deep groove bearing with a flange and puller groove. However, bearing arrangements can become pretty complicated, especially showing preloading and other aspects like angular loading (see attached image).

It would really help if you could come up with very specific questions to ask and possibly one at a time so as to make things easy for everyone to understand.

Last edited: Dec 20, 2007
5. Aug 22, 2007

### Andreii

FredGarvin thank you for your respond. Latex code that you showed, isn't visible for me. I tried with two different Browsers but it says ''Latex image generation failed. The latex source for this image is invalid''.
About the image, with .gif extension, which you showed - I have very similar one in my mechanical engineering handbook but it doesn't really help. One subject is how the (ball) bearing looks like, different subject is how do we draw it on preexisting blank outline (surface).
About the .pdf file - this is exsactly what I had in my mind for bearings. However, the surface is very complicated here. Usually when we have the task with bearings to put on the surface, preexisting space (lets say, given by teacher) contains max 15 lines. I know when it comes to bigger drawings such as drawing of whole machine, the students need to do everything alone - nothing is given and there are also many other elements on the surface.

I know my question wasn't specific at all but I would just like to know how do we draw on given surface screw thread (steps that student needs to do to get the drawing on the picture which I showed from my mate) and bearing? Is there any tutorial?
I have been searching around but everything what I get are tables, few definited dimensions and pictures how bolts look like in reality.

I also apologize for my English language, I know Im not fluent in it but studying on our mechanical engineering university is extremly hard for me and since I have already successfuly passed the English language exam, Im rather focused on other subjects to do successfuly also than going on some more additional English language lessons.

6. Aug 22, 2007

### FredGarvin

Andreii,

I think I fixed the LATEX code now.

I will look around and see if I can find anything that isn't copyrighted to show. A good book that would have all of your answers is ASME Y14.6-2001. It is a standard printed by ASME. Again, I also HIGHLY recommend that you try to find a copy of Machinery's Handbook:
http://www.industrialpress.com/en/MachinerysHandbook/default.aspx

http://www.ic.arizona.edu/ic/ce210/fastener.htm

At the bottom is a pretty good cross section of a stud with a drilled and tapped hole. That is very representative of what you would see in a cross section (without dimensions or notes).

As far as the bearing is concerned, are you wanting to show it in cross section or in a pictoral type of view? The view is completely dependent on what you need to show in the drawing. Can you go into a bit more detail of what you wish to convey in your drawing of a bearing?

P.S. You're doing pretty darned good with your English. It's a lot better than I would do if I had to post in French or German.

7. Aug 22, 2007

### Andreii

Ok, I already got my copy Machinery's Handbook 27th Edition.
I looked at the page http://www.ic.arizona.edu/ic/ce210/fastener.htm. I see I can get few datas from drawings here but not many – Im not sure why are used those four cutted lines HERE and if we look at the picture wich I posted, also one part of '' bolt's head '' is missing. I don't know description of the task – it isn't on this site, so it might not be necessary to include this part of head into the drawing. From the same site but on THAT picture I can see that my statement number 2 was prolly correct but if we look at the entire link which you posted, and scroll down to bolt M20x1.5 there might be two errors on the site – first is: the bolt M20x1.5 doesn't exsist, does it? The length cannot be only 1.5 mm. The second one: as far as I know, 65mm cannot be any length in this ''bolt''. It might be large possibility that my understanding is wrong – I wouldn't be able to do the screw thread as my mate did (on the picture in my previouns post), at least not yet.

For the bearing(s) – usually we don't need to show machine elements in cross section. You have attached the file Bearing Examples.pdf before. Im interested for pictoral type of view as shown in .pdf, I just need to know four important topics about bearings:

- where exsactly do I need to put it on the drawing
- which type of bearing do I have to use (often is this data already given in description of the task)
- how many bearings should be used
- how exsactly do we need to draw them (what kind of position – how do we turn it / them, do we need to care for any angles, how far from the closest line – in case of already given pre-existing outline as known as surface, how far from closest machine element – in case of more complicated drawings,…)

I was interested about ''less complciated'' surface with 10 or 15 given lines maximum, I know you prolly just wanted to show me some examples for those bearings, but Im afraid Im far far away from being able to design drawing such as those ones, in that .pdf file, are. :(

Last edited: Aug 22, 2007
8. Aug 26, 2007

### Andreii

I didn't mean to rush but may I just ask, does anyone still read this topic?

9. Aug 26, 2007

### Danger

I am, but I have nothing further to contribute. I look at a thread if there's a new post indicated or if I think of something relevant.

10. Aug 26, 2007

### mgb_phys

I will try and understand -
With metric bolts the M20x1.5 specifies the diameter and the thread pitch
M20x1.5 = 20mm diamter to the outside of the threads and the peaks of the threads are 1.5mm apart. You would quote the bolt length separately the 65mm is the length between the underside of the head (called the shoulder) and the end of the threaded part of the bolt.
It is done this way because same tool (tap) is used for making a M20x1.5 hole however deep it will be.

If you mean the extra dotted lines on this caphead drawing:
The inner ones show the diamter of the inside edge of the thread - you wouldn;t normally put these on a drawing of a hole, they are just here to show the full details of the bolt for this specification.
The short outer ones at the bottom are showing that the thread in the hole goes deeper than the end of the bolt, this must be true so that the bolt can be fully tightened before running out of thread. The triangle end of the hole just shows how deep it is drilled.

On a real drawing you would show the hole as the outside diameter of the thread 9ie 20.0mm for M20) and draw a hidden detail (dashed line) 1.5mm inside from each edge, you would then label it M20x1.5 x however deep you want the thread.

In metric there is also a standard or typical pitch for each thread size, so you could just say M20 and the machinist would use the most common pitch (which is I think 1.5)

11. Aug 27, 2007

### FredGarvin

Andreii,
I have to admit that I have reached the end of my ability to understand what you are asking with respect to bearings. Where exactly do you need to put them on the drawings? One thing I do understand is that you are trying to understand bearing selection. That is an art form in and of itself, not related to engineering drawings. Bearings are a very technical aspect that requires a lot of knowledge to select the proper type and mounting/lubrication scheme as well as housing and mounting fits/tolerances. Most of these answers can be had by asking the bearing manufacturer for the information after you give them your intended use and design. I can not answer all of that in one post.

As far as how do you need to draw them, it is up in the air. I know some designers that like to show bearings in their loaded condition, i.e. angular contact bearings. Some designers do not. It will ultimately depend on your company's procedures or your own preferences after you have gained some experience.

12. Aug 27, 2007

### Andreii

mgb_phys: Thank you for your respond. In M20x1.5 I understand first parameter (20) is external diameter and the second is length but length of the bolt cannot be 1.5 mm? You mentoined 65mm - May I ask you where have you got that data? I checked all my books but nowhere is definited that length.

I went to assistant of teacher on his ''Time For Students'' and he explained me few subjects what I have done wrong. My new drawing of screw thread M10x40 is HERE
I know it isn't 100% finished yet due to part of the drawing that I marked with two red circles HERE2

If I compare with other, similar task that I showed above, I changed surface a bit to more complicated but now I don't know how to end both lines (external diameter of bolt) - showed with those two little red circles. Do I just make little horizontal line (on both side of course) towards internal diameter of bolt?
As it is visible, I removed one preexisting outline (part of surface) but Im also in doubts now for length of this external diameter of bolt. That length is well visible with green color HERE3. Is it definited how far do I need to draw it?
Also, I searched for the expression of the part of bolt's head in yellow color - it is Washer. Is this normally that diameter of ''Washer'' is smaller than diameter of bolt's head. I ask that because when the bolt gets its torque, in the ''Washer'' needs to be some empty space and therefore diameter of it should be bigger than diameter of bolt's head. Or is it fine as I drawed?
I didn't care much about end of bolt (red circle on the latest link which I showed) - it isn't definited in the book so in that part I just cared that 40mm bolt length will be made. Is this OK also?

Thank you!

P.S.: I tried to reread some rules on the forum. I hope I don't annoy too much or make any troubles or anything against the rules with my ''How To Draw'' topics. I know I have been mentoining mechanical engineering drawing before also but we have to draw a lot on our university.

13. Aug 27, 2007

### mgb_phys

As I said when you quote a THREAD you specify the diameter and the pitch M20*1.5 is a 20mm diameter by 1.5mm PITCH ( ie the the distance between points on the thread).
If you specify a BOLT as M20x40 it means a bolt 20mm in diameter by 40mm long.
Because you don't specify a pitch the user would have to guess if you meant M20 Fine (with a 1.5mm pitch) or M20 Course (with a 2.5mm pitch).
For many typical size bolts there is usually a standard pitch ie 1.0mm for M6 and so you don't have to specify the pitch if you want to use this one. So you can safely say M6x40 for a 60mm long M6 bolt, for unusually threads which are very large or small it is safest to specify what thread you want.
The 65mm long was just an example it doesn't mean anything.

For each thread size you will see 2 other sizes quoted a
"tap drill" - is smaller than the thread, this is the drill you need to make the whole before you cut the thread, so for M20 it is probably 17-18mm. For large bolts it depends on the material and type of tap.
"clearance drill" is the size of the hole you need to drill to allow a bolt to pass easily through. This is the size of the inner hole in a washer, because this must pass over the thread.
These drill sizes will be listed in any machine handbook, you should know them for typical metric bolt sizes.

The outer size of the washer will depend on the application. It might only be 1-2mm large in diameter than the bolt head. Or for putting bolts into very soft materials you would use a much larger washer to spread the load over a bigger area.

I can't really understand the questions about the pictures - they are out of focus.

You aren't breaking any of the rules in the forum and we are glad to help, we are just having problems understanding your english and your long involved questions.
It also isn't clear if you are simply asking how to draw things or how to design them.

14. Aug 27, 2007

### Danger

There are three main reasons for using washers, which determine what size they should be. The first is for stress-relief, wherein the washer distributes the force over a wider area of the parent body. An example of that would be when bolting a couple of pieces of wood together. An 'unwashered' bolt head would dig into, and possibly pull through, the material. In that case, the washer must be quite a bit larger in diameter than the bolt.
The second reason is to protect the surface from abrasion by the bolt head, such as when bolting a couple of nicely painted things together. The size doesn't matter in that case, but the washer should be of a softer material such as plastic or aluminum.
The third reason is when the washer is used as a locking device to keep the bolt from loosening in use. That requires some sort of 'springiness'. That's most often achieved by having the washer split and bending the ends of the ring slightly apart perpendicular to the diameter. The effect is twofold. To start with, it pre-loads the bolt in the 'undo' direction against the female threads, thus binding it to some extent. Secondly, the ends dig into both the underside of the bolt head and the parent material.
Another reason for washers, which should be used only in an emergency situation, is to effectively shorten a bolt that's too long for the purpose. If you have a blind hole, for instance, that's 1/2" deep, and have only a 3/4" bolt available, you can stack up 1/4" of washers under the bolt head to keep it from bottoming out. Again, though, that's a very bad construction practice that shouldn't be used unless absolutely necessary.

edit: Mgb, you sneaky bugger! Beat me to it again.

15. Aug 28, 2007

### Andreii

Ok, I see I haven't been understandable enough with my questions. Thank you anyway for your time for me.
Before I ''end'' this topic, I have one question for you Danger.

With your sentence, I understood that you prolly mean the mainly diameter of the bolt and not the diameter of bolt's head.
Talking about bolt's head and washers. What if the diameter of washer was smaller than diameter of bolt's head? In the accordance to engineering standards (tables) - even the books show washer's diameter smaller than bolt's head. I think this is fine but I would like to make sure...

16. Aug 28, 2007

### mgb_phys

The inner diameter of the washer is larger than the threaded part of the bolt - usually a little larger than the clearance drill. The outer diameter of the washer is bigger than the bolt head, because it's job is to spread the load over a large area - as danger said.

Sometimes you use spring washers that are smaller than the diameter of the bolt head, these can go into a counterbored hole and keep the bolt tight.