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bhjones
05-07-2009, 01:18 PM
I've recently added a #44 Dumore to my tool cabinet and while playing with it the other day I wondered if this was something that's ever done with a TPG.

lazlo
05-07-2009, 04:22 PM
I've never seen DIY thread grinding, but it was the subject of an amusing exchange between Geo Thomas and Professor Chaddock in an old Model Engineer (Chaddock claimed that you can thread grind in the Quorn).

A big issue that I see is that thread grinder have giant grinding wheels that are dressed to the 60* angle, so the wheel doesn't need to be re-dressed very often (to keep the proper thread form).
With a little toolpost grinder wheel, you'd probably need to dress the wheel a lot...

lane
05-07-2009, 07:11 PM
Yes Never ground any from start to finish. But rough out with thread tool and finish after heat treat . But I do not think you will want to Its a bitch.Would not want to have to do any more . That being a Fact.

lakeside53
05-07-2009, 08:48 PM
Maybe a good use for CDN wheels?

How does a large grinding wheel deal with the lead angle? My first thought is that it would need to be a very small wheel, but...

lazlo
05-07-2009, 09:39 PM
Maybe a good use for CDN wheels?

Yeah, but have you ever seen a 60* CBN wheel? You can't form dress a CBN wheel like you can with an AO wheel.


How does a large grinding wheel deal with the lead angle? My first thought is that it wold need to be a very small wheel, but...

They tilt the whole "saddle" (whatever you call that on a thread grinder :) ).
Look at the size of the white thread grinding wheel:

http://www.gearmachines.com/applications/CatalogManager/images/2308.jpg

10KPete
05-07-2009, 10:18 PM
So one would need to have an angle shim for each size/pitch of thread to get the wheel on the correct helix angle.

Could be done. I suspect that a guy would only need a couple-three made as needed.

Pete

lakeside53
05-07-2009, 10:46 PM
I use CBN every day to grind chainsaws chains. Surely you can buy a 60 degree CBN... What do the "big guys" use for thread grinding?


I could mount my TPG on a minature sine plate for different threads;)


Oh look... the Chicom guys make them.. which means they must have copied a good old USA brand ;)

http://www.china-superabrasives.com/CBN_grinding_wheel/CBN_flat_wheel_tapered_both_side.htm

Paul Alciatore
05-08-2009, 02:54 AM
So one would need to have an angle shim for each size/pitch of thread to get the wheel on the correct helix angle.

Could be done. I suspect that a guy would only need a couple-three made as needed.

Pete

According to my calculations, a 1 degree error in setting the angle of the wheel would produce only a 14 second error in the angle of the sides of the thread. You could easily set the wheel to within 1/2 degree of the ideal value with a five and dime store protractor. That would limit the error to only 7 seconds.

And the curvature of the screw being ground would prevent any interference above or below the point of tangency.

Before worrying about using sine plates or precision angle gauges, make sure you can check the thread to that kind of accuracy. Heck, you could eyeball the sucker and never even see the error.

A little math (trig) is a valuable thing in the shop.

clutch
05-08-2009, 07:14 PM
We grind ~ 2" shafts hardened to ~ Rc58 all day using a ~2L" x ~2"D cbn wheel.

On a good day we can do 40 shafts before a full dress.

Clutch

lakeside53
05-08-2009, 09:07 PM
You dress CBN? or are you just unloading it with the white ceramic stick?

clutch
05-09-2009, 03:28 AM
You dress CBN? or are you just unloading it with the white ceramic stick?

Rotary dresser filled with diamond. Not sure if synthetic or natural.

Clutch

tdmidget
05-09-2009, 01:20 PM
So ~ what is a "~2L x ~2"D cbn wheel" ? Why is everything ~? Why do you need to dress it? And sounds like you are talking about a brake dresser. Should be used once after the wheel is mounted. RARELY thereafter.

lazlo
05-09-2009, 01:24 PM
Surely you can buy a 60 degree CBN... What do the "big guys" use for thread grinding?

Oh look... the Chicom guys make them.. which means they must have copied a good old USA brand ;)

http://www.china-superabrasives.com/CBN_grinding_wheel/CBN_flat_wheel_tapered_both_side.htm

Hey, that's nice! I wonder if they make them in acme thread form? Seems like that would actually make it feasible for a HSM'er to do thread grinding...

juergenwt
05-09-2009, 02:54 PM
DuMore made a No. 5 TPG with a dressing attachment for grinding threads. We used to have one and I will see if I can still find it on my next visit. Here is how it worked:
No. 5 DuMore TPG on a attachment mounted on the lathe tool post. The large mounting hole of the grinder would slide on a horizontal shaft of the attachment and lock in place. The grinder was now mounted with the motor on top and the spindle parallel to the ways. You could now tilt the grinder to the correct lead angle using a graduated mounting plate of the attachment. There was a height adjustment on the attachment so the wheel could be centered after setting the lead angle.
A dressing attachment consisting of two small diamond mounted on each side of a 60 deg slide (looks like an upside down "V") with a scissor type lever alternately moving the two diamonds at 30 deg on the left and right side of the wheel. This was mounted on a small graduated plate for setting the moving diamond to the lead angle. The whole dressing attachment was than mounted on a long bar clamped to the spindle of the tail stock.
You would lock your tail stock and move the compound with the grinder back until the wheel was between the two diamonds and dress the wheel to 60 deg.. Now set a stop on the tail stock side of the compound so you could always come back for a re-dress.
It was actually very easy to set this up - a few minutes.
However we never ground a thread from solid, always pre-cut with a tool bit, left oversize and than finish ground.
If I can still find it I will take a picture. Could be somebody has the same DuMore?

clutch
05-09-2009, 04:54 PM
So ~ what is a "~2L x ~2"D cbn wheel" ? Why is everything ~? Why do you need to dress it? And sounds like you are talking about a brake dresser. Should be used once after the wheel is mounted. RARELY thereafter.

Well, I'm not calling out exact dimensions. We hold 0.0002" for cylindricity. Induction heat treated parts with distortion and a specific heat treat profile. The shaft is a bearing race in the product we make.

Clutch