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Making a d bit reamer question...

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seanol:
Hi,
I am trying to get some info on making a d bit reamer. I have G. Thomas' two books but I have a need for some clarification on some points.

I need a .250 and a .375 reamer. If I purchase drill rod (or silver steel) will it be sized correctly? Could I turn a larger piece to size and hope to get close? (tough question since you have no way of knowing my capabilities I know...)

With the stock the right size I believe the text indicates removing about .001 to .003 material past center and grinding about 7 degrees of clearance. At that point I am thinking that I will heat to a non magnetic state, plunge into water straight up and down. Polish and heat to a straw color at the tip and stone an edge.

Is it that easy?

I know that 2 reamers are relatively inexpensive but SWMBO will not cut loose any funds for toys. The use for these reamers is to ream the holes on a conrod for a .60 Crusader engine I am building. I can get to within .001 on turning usually but I am worried about spring of the work piece and I don't think I can grind a boring bar that small.

I am excited if it works out because I do like the idea of making tools instead of buying them. I just don't want to bite off more that I can chew and I have no way to currently measure a bore that small accurately.

Thanks for looking,
Sean

DavesWimshurst:
Sean,
The drill rod Ive purchased has been on size or even a little oversize, much less than a thousandth.  It is hard to get a real smooth finish when turning down from a larger diameter.  Assuming you get your reamer made you still won't know the exact size it will cut until you try it in the material your using for the rod.  Making a test piece is one way to know.  A plug gauge turned in free machining steel can be used to test the size,  turn the first 1/4 inch to 0.001 smaller,  then a step of the target size and a step of 0.001 oversize.  However you finish the holes do them first and fit the shaft to the hole.

Regarding heat treat for drill rod your basically correct for the water hardening type,  oil hardening is quenched in oil which is less drastic than water.  I usually use the water hardening.  You are supposed to hold the red heat for several minutes,  what I do is heat to non magnetic and try to maintain that color for about five minutes or so then quench in water.  It should be harder than a file at this stage.  Then sandpaper the tool avoiding the actual cutting edge and temper by gently heating the shank end watching the colors travel to the tool tip.  Practice on a piece of similar size to your tool

An easier style of reamer just has the end ground off at an angle,  I've seen reamers discussed on this and other boards before, try the search function.

One other point is these tools won't stand up to much heat so grind carefully and keep the cutting speed down.

I hope this little bit helps,  I've made lots of small tools from drill rod, most successful, and some failures but you never know till you try.

Dave

sbwhart:
Hi Sean

When you section the reamer you you make it a 2 to 3 thou above centre.

One tip for when you anneal it back, the colour changes come on you very very quickly, one way to slow the change down is to anneal it on a bed of sand, just put some dry sand in a tin put the reamer on top and heat the sand from underneath and watch for the colour change.

Good luck

Stew

seanol:
Guys,
Thank you for your advice.

DavesWimshurst:
If I turn to slightly oversize, cut and harden, can I grind it to size in the lathe? I am going to mount the dremel tool I have in my tool post and I was going to slowly approach size, checking with a micrometer. Will this have accuracy issues outside of .001? I just reread the section on boring tools and found I did err on the wrong side of center. My idea is to grind to size, lock the headstock of the lathe and use the cross slide to grind the side and back relief at the the 6 degree angle. Then I was going to grind the face down to about .006 above center.

Since the con rod is aluminum and the crank pin is steel I am thinking that the fit might not be that critical. Is .001 good enough?

Could you get a tight fit and lap to size on the crank pin itself?

sbwhart:
Thank you for the tip. I don't have a tin to heat up, could I use some mild steel with sand on top? My idea would be to set a plate of .375 material on 2 fire bricks and heat from the bottom with the part on a bed of sand on top. How do you go about making the heating even?

Thank you both for your help and I will document the making when I get to it.

Regards,
Sean

sbwhart:
Hi Sean

Putting it on a pile of sand will be OK what your doing is increasing the mass your heating up slowing down the rate rate of temp change.

Have fun

Stew

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