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  #11  
Old 03-20-2018, 06:15 PM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
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Mehrdad,
I think you need to get all of the chipped areas out of the holes you've drilled. A chip is a stress riser, and under the right conditions of temperature and load near the hole, it will crack. If additional countersinking won't get rid of the chip, you'll need to drill a larger hole with a clean cut. Countersink this hole, make it smooth, and if it's larger than the head of the installed rivet - not to worry.... use a countersunk washer to capture the rivet head and spread the load out to the hole. I made all my drilled holes in my canopy 2X the diameter of the rivet shank to allow movement. Not only countersinking, but polishing all cut and countersunk edges in the plexiglass will reduce stress riser areas, and allow easier movement with temperature changes. Make sure you use soft pull rivets for canopy installation if you are using rivets for attachment - not the best plexiglas attachment method by the way. You can't regulate the pull on the rivet, and even 'soft pull' rivets pull too tightly.
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  #12  
Old 03-20-2018, 07:46 PM
judoka5051 judoka5051 is offline
 
Join Date: Aug 2010
Location: Stuart, FL
Posts: 211
Default EAA videos!

There's an EAA video on this subject. He even shows you how to modify a standard bit. This is the method I use, and I drill hundreds of 9/32 holes in plexi every week.
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  #13  
Old 05-17-2018, 09:39 AM
RobB52 RobB52 is offline
 
Join Date: Nov 2013
Location: Shreveport, LA
Posts: 45
Default Enlarging holes?

I am ready to drill my back window and see several different techniques. I checked what Vans published and found the following in 5.19:

- To enlarge holes the use of a step-drill (Unibit) or reamer is recommended.

- CAUTION: Using a regular twist or plexi drill to enlarge a pre-drilled hole is not recommended and will practically guarantee a cracked canopy as a result.

So if I follow Vans guidance, I should not use a plexi drill to enlarge holes. I have looked for a step drill that goes from 40 to 36 to 27, but apparently that does not exist. The only other option above from Vans recommendation is to use a reamer. I have a 36 and 27 straight flute reamer. I have seen no one on the forum mention using a reamer to enlarge the holes.

Two questions:
1. Has anyone used a reamer to enlarge the 14 plexiglass holes from 40 to 36 to 27 as the plans dictate?

2. What am I missing on the unibit guidance and how do I use a unibit on such small holes?

-------------------------------
Rob
RV-14 Finish Kit in the Works
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  #14  
Old 05-17-2018, 11:23 AM
Bavafa Bavafa is offline
 
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 2,287
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Quote:
Originally Posted by RobB52 View Post
I am ready to drill my back window and see several different techniques. I checked what Vans published and found the following in 5.19:

- To enlarge holes the use of a step-drill (Unibit) or reamer is recommended.

- CAUTION: Using a regular twist or plexi drill to enlarge a pre-drilled hole is not recommended and will practically guarantee a cracked canopy as a result.

So if I follow Vans guidance, I should not use a plexi drill to enlarge holes. I have looked for a step drill that goes from 40 to 36 to 27, but apparently that does not exist. The only other option above from Vans recommendation is to use a reamer. I have a 36 and 27 straight flute reamer. I have seen no one on the forum mention using a reamer to enlarge the holes.

Two questions:
1. Has anyone used a reamer to enlarge the 14 plexiglass holes from 40 to 36 to 27 as the plans dictate?

2. What am I missing on the unibit guidance and how do I use a unibit on such small holes?

-------------------------------
Rob
RV-14 Finish Kit in the Works
Rob,
The issue with using a unibit, unless you can find one that has the adequate depth for each step, is that it works well for thinner material but for thicker material as you go deeper, you will get to the next size.

Take a look at a Plasdrill bit and Tap plastic has a video of it that shows how clean they drill into plastic. I have them and I can attest to the job they do. The only thing is that they don’t come in a letter type drill bit and the closes size to the #27 is a 5/32” which is slightly larger than #27.

https://www.youtube.com/watch?v=9mxZMXCjDuA

On parts that you can support the back of it, like the back window, have a person to protect the back side of the window that is being drilled with a piece of wood. This method will greatly reduce the chance of chipping.

I have drilled many pieces (both practice and actual) with a #40 and then finished it with the Plasdrill. I even used the 5/32” bit on the hole that I had got the chip and it took out the chip cleanly.

McMaster has #27 drill bit for plastic but it was a disappointment as they did cause chip. Finally warmer temp is your best friend.

Good luck
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  #15  
Old 05-17-2018, 11:30 AM
Stockmanreef Stockmanreef is offline
 
Join Date: Nov 2012
Location: Midland, mi
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The hole made by the 36 bit is to tap the plexiglass and the roll bar at the same time. Could you skip this and just match drill a #40 hole, then drill out and tap the roll bar with a #36. Then just go from a #40 to a #27 in the canopy? I know that the recommendation is match drill #36 canopy and roll bar so you can tap the canopy and roll bar together to get a straighter tap.

Wouldn't a reemer suffer from the same issue as a regular drill bit. In that, the point when the hole is enlarging at the back side there will be a point with a very thin piece of plexiglass that would chip off. That is why a drill bit with the outer edge sanded off helps alleviate this issue.

Is there a potential issue with cracking when tapping the hole in the canopy?

I also plan to use the following to counter sink. I figure that grinding the counter sink would be better than cutting.

https://www.permagrit.com/kt2/

Also cabinet scrapers seem to be a great tool to finish off edges.

I plan to start canopy soon, so I am very interested in this topic.
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  #16  
Old 05-17-2018, 12:01 PM
Mike S's Avatar
Mike S Mike S is online now
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Mehrdad, are you aware of this place-----right off Missouri Flat Rd.

https://www.fabricationtoolsandmaterials.com/index.htm

Great place for tools, cleaners, and advice.
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  #17  
Old 05-17-2018, 12:15 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,513
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Quote:
Originally Posted by Stockmanreef View Post
The hole made by the 36 bit is to tap the plexiglass and the roll bar at the same time. Could you skip this and just match drill a #40 hole, then drill out and tap the roll bar with a #36. Then just go from a #40 to a #27 in the canopy? I know that the recommendation is match drill #36 canopy and roll bar so you can tap the canopy and roll bar together to get a straighter tap.

Wouldn't a reemer suffer from the same issue as a regular drill bit. In that, the point when the hole is enlarging at the back side there will be a point with a very thin piece of plexiglass that would chip off. That is why a drill bit with the outer edge sanded off helps alleviate this issue.

Is there a potential issue with cracking when tapping the hole in the canopy?

I also plan to use the following to counter sink. I figure that grinding the counter sink would be better than cutting.

https://www.permagrit.com/kt2/

Also cabinet scrapers seem to be a great tool to finish off edges.

I plan to start canopy soon, so I am very interested in this topic.
The recommendations in the construction manual were chosen for very specific reasons.
Largely out of experience helping builders try and recover from some level of catastrophy during their build.
It doesn't mean it is the only way but if you deviate, make sure you understand what you are doing.

Example - The purpose of starting with the window and roll bar at # 36 is to help builders get a properly aligned tap. This helps alleviate broken taps and crooked holes (both cause their own different problems)
#40 is bigger than # 36. If you start with 40 in the window you have another potential for misaligned holes (more problems).

The thing to keep in mind drilling acrylic is that a standard drill bit wants to pull through the soft material like a screw. It does it even worse if you are enlarging an existing hole.
The way to minimize problems is to only drill with a tool that primarily uses a scraping action to remove material (like a step drill or plexi drill)
You can modify any regular drill bit to remove material this way. A search on line will provide a lot of how too information.
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  #18  
Old 05-17-2018, 01:29 PM
RobB52 RobB52 is offline
 
Join Date: Nov 2013
Location: Shreveport, LA
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Scott,

Just to follow up, the Vans construction manual recommends using a reamer to enlarge the canopy holes (or a unibit) in paragraph 5.19. Does the reamer not cut in a very similar manner as the unibit?

Any comments on that? I happen to have a #36 and a #27 straight flute reamer.

I will drill some practice pieces and see what it does when I get home.

Thanks for your comments.
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  #19  
Old 05-17-2018, 01:51 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by RobB52 View Post
Scott,

Just to follow up, the Vans construction manual recommends using a reamer to enlarge the canopy holes (or a unibit) in paragraph 5.19. Does the reamer not cut in a very similar manner as the unibit?

Any comments on that? I happen to have a #36 and a #27 straight flute reamer.

I will drill some practice pieces and see what it does when I get home.

Thanks for your comments.
Yes, a reamer has similar cutting action as a step drill which is why both are recommended as options.
As mentioned, drill bits can be easily modified to cut in a similar way as well, though they do require care because the spiral flutes are still bale to grab the material and draw it in, if you don't maintain alignment.
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  #20  
Old 05-17-2018, 02:50 PM
Bavafa Bavafa is offline
 
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 2,287
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Quote:
Originally Posted by Mike S View Post
Mehrdad, are you aware of this place-----right off Missouri Flat Rd.

https://www.fabricationtoolsandmaterials.com/index.htm

Great place for tools, cleaners, and advice.
Mike,
I did not know and many thanks for pointing it out.
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