A Question On Machining

May I suggest that you go on ebay and find a small boring bar? Micro 100 sells some really nice ones that will do this job easily.

The reason I suggest boring is because a reamer will follow a crooked hole. It will have a nice finish but the hole may not be straight. A boring bar will cut the hole straight AND give you a good finish; how accurate the bore will be depends on your skills when you bore it.
 
Are you using inch or metric measuring tools? There is a considerable difference between .o25 MM and .025 inches, 25.4:1 exactly.
.025MM is 0.0009 inches.

Or as my delightful Windows Calculator tells me. 9.84251968 to the -4

point25mm_zpsln77n16w.jpg
 
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prasad said:
Thanks Mikey, that makes some sense. It is possible that my TS or drill chuck held in the TS is not aligned with the spindle. I am not sure if I can bore a 5mm diameter hole. However I do find McMaster selling 5 mm reamer. I will order one. I will also do the reaming by hand first, then mount it in the chuck, indicate it as best as I can before facing. I have to get new stock too.
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Before you go making a new part, would it be possible to bore out the center and press fit a bushing it it? If so, you can drill and bore the bushing, reface the part and you're done.
 
Bill Gruby said:
Is that a typo, 0,25?? 0.25 is 1/4 inch, or am I not seeing something??

"Billy G"
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I do everything in inches but the stepper motor I have has a 5 mm shaft. I measured it to be slightly larger than 5 mm. I ordered a 5 mm drill bit that I used for drilling.
 
Hope you get it straightened out ! Is this a welding turntable ?
As a last resort, you could also weld that hole closed and start over ...although the welding might cause distortion across the large flat disc . Need alotta chill blocks ...
Nice project either way !
I'd love to see the plans .
All Too often I could use a turntable for welding.

Steve , Northeast PA ...coal country
 
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If your tailstock is slightly off center, the drill bit may find the center but can cut at an angle. The angle won't be much but being magnified by the 6" diameter will create a fair amount of wobble. The tailstock, including the drill chuck must be aligned with the spindle, both horizontally and vertically. Additionally, the drill bit must be straight. Both drill bits and reams are fairly flexible. A ream tends to follow a drilled hole so it will not correct a hole that is misaligned.

For precision alignment, I would bore the hole. You can make a micro boring tool from a broken tap or drill bit. Had one for years that I used to bore holes as small as .1" diameter. Drill a pilot hole as large as you comfortably can without cutting into the finish diameter. You will be able to make a precision diameter hole which is true to your disk. If you don't have a set of pin gages, turn some test pins which are slightly smaller in diameter that your finish size to allow you to sneak up on the final size. Use a micrometer to verify the diameters if you have one.
 
Drilling is a roughing operation. It just removes bulk material. It does not make a hole to size or locate the hole accurately. To locate a hole accurately requires it to be bored after drilling or otherwise opening up the hole. Boring is poor at removing lots of material and is poor at meeting a precise hole diameter. Reamers do not start holes, and do not locate holes accurately. Done properly, reaming finishes a hole that is round and to size. The process, then, is to drill the bulk material, bore the hole in the correct location but a bit under size, and then ream the hole for the final dimension and accurate roundness.
 
I was also wondering if it was for a welding turntable, I have built several of these for tig welding, my next one will be with a stepper motor.
I too am curious as to what it will be used for??
I dont see a mention of a center drill to drill a pilot for the drill so that it starts centered in the hole?
As mentioned in previous posts drill bore then ream and the hole will be straight. Also how the motor shaft is pressed into the plate will make a difference as well, everything should be done squared up in a press as it can press, as it can be a bit crooked as well especially on a steel shaft that small into an aluminum plate of that diameter.
 
Personally if I need a center hole 90° too two parallel sides I will drill my center hole & bore it to size. Then I make a mandrel with a center hole on both sides & turn a slight taper on it between centers. I then put a spot of Crazy Glue on the mandrel & press it in the hole. Turning the the mandrel between centers I cut the two surfaces 90° to the center then the outside concentric to the center. A little heat & the mandrel falls out.

ETA: Careful cutting because if you get the part hot cutting the mandrel will come lose.
 
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