Threading #6-32 UNC Hole in Plexiglass - DIY Guide

Click For Summary

Discussion Overview

The discussion revolves around drilling a hole for a #6-32 UNC bolt in plexiglass, focusing on hole size, threading requirements, and considerations for using nuts. Participants explore various drilling techniques and the implications of using plexiglass in this context.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant inquires about the appropriate hole size for a #6-32 UNC bolt and whether threading is necessary when using a nut on the opposite side.
  • Another participant provides links to tables for tap and drill sizes, suggesting that a clearance hole is needed rather than a tapped hole.
  • A participant cites their Machinery's Handbook, stating that a normal fit clearance hole for a 6-32 screw is a #18 drill (.170") and a close fit is a #23 drill (.154").
  • There is a suggestion that drilling a hole of .154" would allow for a tight fit with the bolt and nut, prompting a follow-up question about the implications of hole size on stability.
  • Concerns are raised about aligning multiple holes and the need to consider tolerances if multiple holes are involved.
  • One participant warns against bolting plexiglass, especially outdoors, due to its high Coefficient of Thermal Expansion, recommending oversized holes and specific tightening techniques to prevent cracking.
  • A later reply clarifies that the project will be indoors, reducing concerns about temperature variation and mentioning the use of two layers of plexiglass with load cells in between.

Areas of Agreement / Disagreement

Participants express differing views on the best practices for drilling and bolting plexiglass, with some advocating for specific hole sizes and techniques while others caution against bolting altogether. The discussion remains unresolved regarding the optimal approach for this application.

Contextual Notes

Participants reference various sources for drill sizes and techniques, but there is no consensus on the best method for drilling and securing bolts in plexiglass, particularly concerning temperature effects and alignment of multiple holes.

JD88
Messages
108
Reaction score
0
Probably a stupid question but...

I have a device with a bolt that is designated #6-32 UNC. I need to drill a hole in a surface to for this bolt to fit into. How big should this hole be? If the material I am going to be threading the bolt into is plexiglass do I need to thread the hole I drill? I plan to put a nut on the other side.
 
Engineering news on Phys.org
JD88 said:
I have a device with a bolt that is designated #6-32 UNC. I need to drill a hole in a surface to for this bolt to fit into. How big should this hole be? If the material I am going to be threading the bolt into is plexiglass do I need to thread the hole I drill? I plan to put a nut on the other side.
Is this what you want?
http://www.boltdepot.com/fastener-information/US-Tap-Drill-Size.aspx
This is a more complete table:
http://www.marfas.com/machinescrewtapping.shtml
 
Last edited by a moderator:
Because he's using a nut on the other side, he needs a clearance hole not a drill size for tapping.

I use my Machinery's Handbook (27th edition) for all such things. In clearance holes on page 1621, a "normal fit" clearance hole for a 6-32 screw is a #18 drill, or .170". A "close fit" is a #23 drill or .154".

I found this table of tap and clearance hole values: http://www.stanford.edu/~jwodin/holes.html

It has somewhat smaller sizes quoted than in my Machinery's Handbook, but it looks like they would work in a pinch.
 
Last edited by a moderator:
Mech_Engineer said:
Because he's using a nut on the other side, he needs a clearance hole not a drill size for tapping.

I use my Machinery's Handbook (27th edition) for all such things. In clearance holes on page 1621, a "normal fit" clearance hole for a 6-32 screw is a #18 drill, or .170". A "close fit" is a #23 drill or .154".

So does that mean that if I drill a clean hole that .154", my bolt will fit nice and tight in there and then when I put the nut on everything will be nice and sturdy?
 
Is it just one hole or do you have to worry about multiple hole being aligned? If it is just one hole and you want it pretty tight, you can get away with going the next drill size up from the .138 (I think). That's going to be pretty darned tight. I would recommend not going below the .154 though.

If you have multiple holes to align, you need to look at the tolerances of the bolt hole positions and what your machining can achieve to establish the hole size.
 
Bolting Plexiglas is not recommended, especially if used outdoors, with a large difference in temperature. The reason is it has a large Coefficient of Thermal Expansion, about four times as much as aluminium. If it is not allowed to expand and contract it will crack.

If you must use bolts: cut the panel with 1/8 to 1/4 inch clearance and holes should be drilled about 1/8 inch oversize. Screws should be tightened down and then backed off one full turn, using elastic stop nuts and large washers.

It works better if you use a drill bit with an included angle of 150 degrees or a unibit drill.
Better method available here:
http://www.altuglas.com/expert/data/116
http://www.rplastics.com/plexdesign.html
 
Last edited by a moderator:
This is going to be inside. I am not worried about temperature variation.

Actually what I am going to need to do is have two layers of plexiglass with three Honeywell Model 31 Load cells in between and attached to each layer.
 

Similar threads

Replies
3
Views
2K
Replies
6
Views
1K
Replies
8
Views
11K
  • · Replies 3 ·
Replies
3
Views
7K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 5 ·
Replies
5
Views
14K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K