Question about Tapping

Reply

  #1  
Old 04-18-19, 04:00 PM
Member
Thread Starter
Join Date: Apr 2019
Location: USA
Posts: 2
Question Question about Tapping

Hello, I am looking for some help finding info about a specific tap.

I am working on piece of equipment that requires four 4-20 x 0.625 plastite pan screws. Currently, they are not fitting into the piece all the way, and I thought using a tapping tool would help the threads go in easier. I didn't have a 4-20 tap tool and looking into it I don't see any options. Are there other options available to make it easier to screw in? I could perhaps change the screw, but I am trying to avoid changing it if possible.

In the picture with the orange plastic example, there is a gap showing. This is what I am trying to avoid and need for those screws to go in all the way.

Any knowledge would be helpful, thank you.

Name:  t1.jpg
Views: 77
Size:  61.1 KB

Name:  t2.jpg
Views: 70
Size:  61.9 KB

Name:  t3.jpg
Views: 67
Size:  25.2 KB
 

Last edited by PJmax; 04-18-19 at 06:52 PM. Reason: resized pictures/added closeup
Sponsored Links
  #2  
Old 04-18-19, 04:45 PM
Member
Join Date: Jan 2013
Location: U.S.A.
Posts: 1,701
Likes Received: 2
Hang on for a bit in case someone else has an idea that you like better, but here's how I would approach it and I don't too often back myself into the corner. First off, I would want the hole to be the minor diameter of the screw, meaning that of just the shank, at the bottom of the threads. If the screw is tapered, I would measure this at about halfway along the threads. So you're not going to tap it, but may have to open it up a tad. Second, I would lightly lube the screw threads, and for something like this would use a bar of soap.
 
  #3  
Old 04-18-19, 06:57 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 50,096
Likes Received: 75
Welcome to the forums.

You only have a limited amount of picture storage..... so I resized them for you.
I added a closeup of the installed screw.

Based on what aka pedro posted...... it looks like the material the screws are going into is already larger than the shank of the screw unless the close up picture is not your actual piece. Those are basically self tapping screws and should not need to be pre-tapped. I agree 100% with the soap on the screw.
 
  #4  
Old 04-19-19, 03:37 AM
Member
Join Date: Jan 2013
Location: U.S.A.
Posts: 1,701
Likes Received: 2
Yes, much easier to see with the pictures resized. I'm missing something between the first picture and the second and third pictures though, so will mention just the last two. And in that regard I agree with PJ; it looks like the holes in the semi-transparent amber piece are already large enough, possibly even already too large. But with that piece and the black flange separated, do the screws drop into the holes in the black flange? If not, I'm thinking that what you have is a matter of the threads biting into both pieces and binding up. If that's the case, you would need to either open the holes in the black flange so that the screws drop in, or make sure the two pieces are tight to each other before running the screws in.
 
  #5  
Old 04-19-19, 08:30 AM
Member
Thread Starter
Join Date: Apr 2019
Location: USA
Posts: 2
Pedro, PJ, thank you both!

The screws do drop in to the black flange part, they don't need to be screwed through there. I put it up tight against the amber part and attempt to screw it in, but I meet a lot of resistance at the last part, and am unable to screw in completely. I will try some sort of soap/lubricant on my next attempt. The amber plastic is a machined part that is being manufactured for us and we were considering a request to make those 4 screw holes a tad larger. However, you both said that the holes look larger than the screw, but it does not feel that way.

The black plastic in the first picture is the old model of the same part (the broken one). It fit great in that piece, but we have a new manufacturer doing this amber piece. This area currently seems to be the only issue left.
 
  #6  
Old 04-19-19, 09:41 AM
Member
Join Date: Oct 2015
Location: Ct.,USA
Posts: 945
Likes Received: 6
Those are special (not SAE)self tapping screws used when creating threads in soft materials like plastic, wood, etc..Your symptoms indicate the hole with the threads is not deep enough. In trying to drill the hole deeper, you will most likely damage the threads. If you can't get the next smaller length screw (or it is too short) grind off an eight inch from the screws you are using or if room use washers under the screw heads.
 
  #7  
Old 04-19-19, 10:19 AM
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 19,551
Likes Received: 28
Your options are lubrication which is basically a Band-Aid fix instead of choosing the proper fastener and putting it into an appropriately sized hole. But lubrication can be a good option if you only need to do a few of these parts. If you are wed to using those parts and those screws I would try an impact driver. As a last resort you can drill out the holes a little bit but it will be at the expense of holding power. If you have to do a decent number of these parts I would choose a different fastener. There are a multitude of different self tapping screws. One with a cut slot at the tip to aid in self cutting the threads might be an option.
 
  #8  
Old 04-19-19, 10:35 AM
Member
Join Date: Oct 2015
Location: Ct.,USA
Posts: 945
Likes Received: 6
I would caution about using an impact driver. You could strip out the threads or crack the material containing the threads trying to bottom out the screws, Pilot Dane, your response seems to address some type of manufacturing environment. I thought this was a DIY (handyman) forum
 
  #9  
Old 04-19-19, 04:26 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 50,096
Likes Received: 75
Yes.... this thread is in regards to a manufacturing environment and there is nothing wrong with that.
 
  #10  
Old 04-20-19, 04:28 AM
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 19,551
Likes Received: 28
Impact drivers are commonly used on assembly lines. Quite often they are automatically fed with screws and have accurate torque control to minimize stripping. But in a commercial setting stripping out one part now and then often isn't the end of the world because you have a supply of more parts. The key is proper sized holes and proper fasteners so there is a good difference between the torque required to drive the screw and when it's tight. This allows the driver torque to sense the rise in torque when the screw is tight and stop driving before stripping.

If designed poorly the torque to drive the screw is too close to the stripping torque which makes it a slow, tedious manual operation for someone to visually see when it's tight enough. Worse is if the torque required to drive the fastener is higher than what the fastener or part can withstand and the head of the fastener snaps off or strips out or the part strips out before it's tight.

If using a common hand tool impact driver you do have to be very careful when driving. Most cordless impact drivers sold in home centers have no torque limiting so it's all up to the operator to know when to stop. Stay on the trigger a fraction of a second too long and you can strip or break something.
 
  #11  
Old 04-20-19, 11:11 AM
Member
Join Date: Oct 2015
Location: Ct.,USA
Posts: 945
Likes Received: 6
It's obvious the screw is too long or the screw diameter is too large or the screw hole is not deep enough or the screw hole diameter is too small. Check the drawings and parts list to determine the problem and have the design changed or parts corrected. The assembly drawing should also contain the screw tightening torque if essential to the assembly.
 
  #12  
Old 04-20-19, 12:50 PM
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 19,551
Likes Received: 28
The screw can also be the problem. There are screws for plastic have a thin, steep threads that leave more plastic between each thread for strength. The thinner threads also reduce the torque required for installation.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes