Thread: balancing a lathe dog

Ah! Tank slapping. Ever ride a 1970 Mach III Bill?

No Bob I've never had the pleasure.

Was quite scary the first time it happened on the Honda.

Bill

Hi Bill,
It is not as bad on a heavier lathe that's for sure. Any out of balance part is going to affect a machine with less mass more than a machine with greater mass.

On the mars (hercus size) I use the face plate as my drive plate. If the dog throws the lathe out of balance I add a bolt through one of the faceplate slots, whichever one I feel is necessary. By moving the bolt in or out on the faceplate fairly fine adjustment can be made. A test run at top speed will soon tell you if your close.

Cheers
Ew

Bill
I am only guessing but perhaps the Lathe Dog is a bit large for the size of the workpiece.
Cant say I have had this balance problem, but a smaller lathe dog might fix it.otherwise just drop the revs back.
Often its just a matter of getting the feel of the machine & working within its limitations.
Lathe Dogs, come in all sizes, & they can be easily made in a lighter construction.
Some of the old forged ones were just too large & heavy for a small lathe.
regards
Bruce

Bill, on a lightweight lathe

- always use the smallest lathe dog, just large enough to hold the workpiece.
- avoid using steel or cast iron lathe dogs. These are made for heavy industrial lathes, and are invariably too heavy for a light hobbylathe (especially the ones with a bent drive arm). Use Aluminium lathe dogs instead. If you cannot find Aluminium lathe dogs, make your own from plate stock.
- Modify your catch plate to accept balance weights. If using the face plate, add balance weights as necessary. Changing the length of the bolt used to clamp the dog onto the workpiece, is also a way of improving balance.

any slight imbalance is accentuated the faster the rotating bit goes

rule of thumb ....slow down...best to keep to speeds where it doesnt shake and vibrate else things could go flying with disastrous results

Here a comparison of two totally different lathe dogs. I choose two that will clamp about the same workpiece size of around 20mm.

- The one on the right is (I believe) of Chinese origin, made of cast iron and is intended for a heavy duty industrial lathe. it clamps up to 22mm and weighs 196g. It came in a set of three that I bought mail order - I rarely ever use them, they are simply far too heavy for my Hercus 260.

- The one on the left (edit) is made of cast Aluminium and is intended to be used for light duty tasks (like with a light Hobbylathe). It clamps up to 20mm and weighs 22g (with the screw). I use it a lot, for example to turn over small motor collectors. It causes only little imbalance. I bought these back in Switzerland about 30 years ago.

1.jpg2.jpg

I cannot understand how someone can use the lathe dog on the right on a lathe of less than say 3-500kg weight. A lathe of less than 100kg weight would jump off the bench if not bolted down at speeds above 800rpm. On a 100kg lathe, the maximum speed of such heavy lathe dog without extra balancing weights would be about 200rpm. I do not know why it is hard to buy lightweight lathe dogs. Probably no dealer does between centers turning himself. Fortunately it is easy to cut such dogs from a sheet of Aluminium plate. Maybe someone doing home casting may consider running a batch, and offering them for sale? Chris

Here I found an ebay seller that has a set of these beautiful light lathe dogs:
Drehherz / Mitnehmer 6-Stück aus Alu, D= 6mm bis 55mm | eBay

I also found them in the Swiss Bruetsch&Ruegger catalogue (where I bought mine from). They make them in both Anticorodal order no 63600 (8 sizes for 6 to 70mm shafts), and in Brass order no 63620 (5 sizes for 6-40mm shafts). Chris

Thanks for the tips.

I guess one trap for newbies is assuming that all the stuff they got with the lathe (2nd hand) is suitable for use with that lathe.

Will definitely follow up on the Aluminium lathe dog idea.

Looks like its not a resonance issue - with huge wobbles at certain frequencies - its just an unbalanced weight that wobbles more as the lathe goes faster.

Bill

Hi Bill,
don't throw the heavy cast dogs just yet.
Try and get into the dark art of counterbalancing.
At some point in your machining life you will no doubt be required to do this.
All I do is roughly gauge how much weight needs to be bolted to the faceplate opposite the heavy side to negate this effect. You can get in the 'ballpark by putting the headstock in neutral and spinning the faceplate by hand and seeing if tends to stop with the heavy bit at the bottom. If it does, add a bit more weight (or move the weight you already have out further) until the chuck faceplate stops in random positions.
The weights can be old bearings, bits of plate, bits of shaft etc with holes in for the bolt to go through, and through the slot in the faceplate.
Counterbalancing is an important part in machine setup and it's great when you get it right as the lathe can nearly be run at full speed for the part you are machining.

Phil