Enlarging a large hole

[rmaynard 15,514]

I have a blower cover from a K-161. I am trying to modify it for another project and need to expand the diameter of the front opening.

Considering that I don't have a machine shop, how would you suggest that I neatly increase the inside diameter from 6 inches to 6.25 inches?

[wallfish 17,012]

Mark the circle 1/8" from the edge.

 a grinder

You can get metal blades for a jig saw and clamp the saw upside down in a vice

Same for the grinder as it's probably easier to control the piece vs the tool

[Kenneth R Cluley 527]

Drum sander in a drill press. Mark at 1/8" and lock quill. Attach a piece of plywood to table, slide, rotate cover until desired size.

[Racinbob 11,094]

I recently did just that (except to 6.5") with a jig saw. I swapped the electric start goodies on a 181 over to a yank start 161. I had the shroud firmly fastened to the work bench but you might find it easier clamping the saw like John said. You can't see it in this picture but you couldn't tell it was cut. High speed on the blade but slow and easy as you cut. 

 

[rmaynard 15,514]

Thanks for the quick replies. All very good. I'll keep looking to see what others come up with.

 

My idea is to take my 150mm hole saw (should fit inside of the 6" opening) and wrap it with self-adhesive 80-100 grit emory paper, slowly grinding and adding layers until I reach 6.25".

Sometimes these ideas sound good in my head, but in practice not so much.

[Handy Don 12,237]

1 hour ago, Racinbob said:

yank start 161

Bob, This modification to the mid-hitch has me very curious. Can you please explain & add pics from the other side? 😁

[8ntruck 7,016]

22 minutes ago, Handy Don said:

Bob, This modification to the mid-hitch has me very curious. Can you please explain & add pics from the other side? 😁

  Probably a jack shaft for the mower drive.  Round hoods were built before the invention of the front mule drive.

[Handy Don 12,237]

6 minutes ago, 8ntruck said:

  Probably a jack shaft for the mower drive.  Round hoods were built before the invention of the front mule drive.

I don’t see any sort of latching or mower frame, so this appears to be a complete “permanent” replacement  for the round hood style mid hitch, at least on this side, using a permanent bearing. 

[Racinbob 11,094]

50 minutes ago, Handy Don said:

Bob, This modification to the mid-hitch has me very curious. Can you please explain & add pics from the other side? 😁

 

Typical setup for a sickle bar mower guys. Not modified, just rebuilt using components from Surplus Center. The entire mower was a frozen pile of rust when I got it.

The attach-a-matic has to be replaced with the sickle drive setup. 

 

[rmaynard 15,514]

 I think this thread has gotten off the track a little bit 

[ri702bill 8,339]

But, I DO so like the picture of an 854 on Gopher Patrol duty.....    And now, back to our originially scheduled program...

 

[CCW 1,295]

@rmaynard The sandpaper idea has some merit.  Perhaps start with drawing the outside diameter of the new hole with pencil or marker and grind close to the line.  Then use your hole saw and sandpaper to bring it closer and finish with a file.

 

 

[rmaynard 15,514]

2 hours ago, CCW said:

@rmaynard The sandpaper idea has some merit.  Perhaps start with drawing the outside diameter of the new hole with pencil or marker and grind close to the line.  Then use your hole saw and sandpaper to bring it closer and finish with a file.

 

 

Good idea. Thanks

[peter lena 8,634]

@rmaynard  might try curved tin snips , draw , scribe ,your intended increase , try tin snips on a  trial piece , for  actual , cutting ability . done a lot of tin snipping , its a doable  thing , Pete

[Pullstart 62,913]

If you choose to use a drum Bob, the larger diameter will make it easier for keeping a smooth radius.  Small diameter tends to dig more.  You might not want to use too big a hole saw for a drum though, so it doesn’t grab ahold and dance the jig around.  Carbide cutters in a die grinder if they are too closely matched to a hole size will do that quicker than you can lay off the throttle.

[peter lena 8,634]

@rmaynard https://www.eastwood.com/throatless-shear.html?gad_source=1&gclid=CjwKCAiAnL-sBhBnEiwAJRGigsO9dJpnge15hUDibLnzm1gkD33iDt5Yn1ZSIvtwDzD4BsU1HdvJRhoCILYQAvD_BwE&wcid=18669317454&wickedid=629952193648&wickedsource=google&wv=4  , have a metal shop near you ?  used this on a regular basis , put the center hole on over the handle , to da !  made for that  ,   not suggesting you buy this , only a reference for a tool that was made for metal fabrication .  been there done that , Pete

[rmaynard 15,514]

Follow-up

Using the suggestion of  @CCW "start with drawing the outside diameter of the new hole with pencil or marker and grind close to the line" was the method that I used. Then I finished with the hole saw with abrasive attached.

 

Finished project

 

 

Before:

 

 

Grandson Mason loved it. 

 

 

 

[OoPEZoO 525]

That's awesome......well done 

[CCW 1,295]

@rmaynard  Glad it worked for you.  Nicely done.