No Lathe, No Milling Machine, No Problem





Introduction: No Lathe, No Milling Machine, No Problem

About: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying posting things I have learned and done since I got my first ...

This is a heavy duty holesaw mandrel.  The shank on this is 7/16 inch and requires a 1/2 inch drill chuck.  My drill has a 3/8 inch chuck. 

I had to make several dozen 3 inch holes in our soffets (also spelled 'soffit') for ventilation louvers.  I ground the shank flats down freehand so the mandrel would fit my drill.  It worked, but it wobbled terribly. 

(The image is from

Step 1: Build It Back Up

I decided to restore my mandrel, but sized for my drill chuck and on center so it does not wobble.  The first step was to build the shank up again by welding.  A wire feed welder makes this much easier than with a stick welder.  (I did not take photos while I was actually doing this project, so this is a recreated photo.)

Step 2: Replace the Pilot Bit Temporarily

I needed a way to put the mandrel into a chuck so I could spin it on center.  The pilot bit is 1/4 inch.  I loosened the set screw that holds it in place and inserted a piece of 1/4 inch rod in its place.

Step 3: Chucked in the Drill

I put the 1/4 inch rod into my drill chuck.  The mandrel now spins in the drill on center without any wobble.  Of course, you cannot use a holesaw on it like this.

Step 4: Grind Until Round and on Center

I held the drill so the mandrel made light contact with a spinning grindstone.  Hold it so contact with the grindstone does not cause the drill to bump, but the grindstone slowly and smoothly takes away high spots and the shank of the mandrel is round and on center.  Experiment with the speed of the drill to find the speed at which you can hold the drill most smoothly.  If there are low spots and voids fill them with a little additional welding and grind again until round and on center.

Step 5: Making Three Precision Flats

I needed a jig to grind the flats on the shank.  I began with two identical scraps of 3/8 inch plywood.  The rod replacing the pilot bit is 1/4 inch in diameter.  I drilled a 1/4 inch hole through both pieces of plywood.  The hole is very near to the edge of the plywood pieces.

Step 6: One Larger Hole

I ground my shank down to 3/8 inch in diameter.  I drilled one of the 1/4 inch holes from the last step out to 3/8 inch.

Step 7: Mount the Mandrel in the Plywood

Mount the mandrel in the two plywood pieces as shown.  This simple support holds the mandrel parallel to the table surface below.

Step 8: Grind Flats

My grinding wheel is mounted on my radial arm saw.  That means I can slide my mandrel holding jig under the grinding wheel.  It also means I can lower the grinding wheel incrementally.  I ground all three flats to just a bit less depth than I wanted so the last "cuts" could be very light.  This was to insure that each of the final cuts would not be affected to any degree by part of the grinding wheel wearing away during heavier cutting on previous flats.  The hex nut on the mandrel made a handy guide for rotating the mandrel 120 degrees between the three flats.  To grind I simply slid the mandrel and its supports laterally toward the grinding wheel.

Step 9: Done Grinding

Here you can see the shank of my mandrel after I finished grinding.  The three flats are equal.  The round portion of the shank is on the mandrel's center.  The mandrel no longer wobbles in my drill chuck.  Yes, its diameter and strength is slightly diminished, but it will be fine if I do not force the holesaw when I use it in the future.  I did a precision job without the usual machine tools needed.



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    36 Discussions

    Where there's a Phil there's a way. Nothing like the good old we don't have a lathe so grind it solution I always say! The further I went along in your Instructable the more it reminded me of this I did recently:

    To really take material off I used an angle grinder then the file and stones to clean it up somewhat. Now I'm going to have to think if I was running it the right way or not as per some of the comments in your post here.

    1 reply

    "Where there's a Phil there's a way" True enough in Phil B's case, but can I steal that one pfred? My name's Phil too. My main motto is "There's always a better way".

    I do not understand how you were able to ensure that the newly ground flats would be aligned properly (at 120 degrees).

    1 reply

    Notice the hex nut that is part of the hole saw mandrel. It is visible in step 7. I used it as a guide to rotate the shaft approximately 120 degrees. In step 9 you can see how the flats I ground correspond closely to the flats on the hex nut.

    Excellent solution to this problem.  I have an arbor that actually twisted off from heavy use with a 4" blade.  My small lathe was not solid enough to turn the hard section of the sleeve I welded back on.  This little jig is the answer, and using my radial arm saw will act as a surface grinder to return the shank back to center balance.  Thanks a million for the ideas~!

    1 reply

    Thank you for commenting.  I had hoped someone might be able to use some general principles from this Instructable.  I never guessed someone would need to do the same job.  I hope it works out well for you. 

    Thank you.  I have known people who have many tools, but get very little use from them.  I made it my aim to have a few tools and find ways to make them do things the user manuals never tell you can be done with them.

    Use of the radial arm saw as a milling machine....a great idea. I am glad I never sold mine. Thanks a lot for the great idea. I have always wanted a milling machine, and never realized I had one all along! come to think of it, you could do the same thing with a table saw. Thanks again.

    1 reply

    Thank you for your comment.  I have published a number of special things you can do with a radial arm saw.  Search Instructables for "radial arm saw."  I expect you could do this job with a table saw if you set it up carefully.  I hope you continue to enjoy your radial arm saw. 

    Phil, you've done it again!  I can't tell you how helpful your ibles are.  I think I'm going to print all of the tool related ones off and put them in a binder.  I already know some of the the things you post, but I always seem to forget when I'm in the middle of a project.

    8 replies

    Thank you, Barry.  I can mail a CD to you with all of my Instructables on it. I am glad they are useful to you.

    I'm afraid that ship has sailed.  I've even given up on the recovery mission.  But we are building a shed for him, so at least my shop will be cleaner with all of his (AND MY!) things gone.  He has more time to accomplish things than I do these days, so I guess it's only fair.....

    Well now you can take up any ridiculously space wasting hobby you can think of.

    Put the shed on castors without him knowing, secretly move it around a little each day, just enough to notice, then one night roll it in to a hiding place and dig a hole where it was... Follow up with a speech about how your tools and stuff just disappeared out of the shop...

    Yep, I've got the space wasting business all planned out!  My Corvette needs shelter from the elements.  I'm also going this week to pick up my grandfathers '72 Ford F-250.  Rarely do I consider trucks worthy of restoration (I reserve that for sports cars, muscle cars and classic cycles), but this one will be a labour of love.  He ordered it ( with various custom parts) the year I was born ('71), and he (almost) always kept it garaged.

    That's a great idea about the shop, but as it's about 30' x 30' and set in concrete, it'll probably have to stay put.

    It is this "thinkin' outside th' envelope"  that separates th' "machinists" from th' "machine tool operators" !!