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Differences in surface grinders, Kent/Acer/etc. vs. Okamoto

jccaclimber

Stainless
Joined
Nov 22, 2015
Location
San Francisco
I'm tasked with specifying a surface grinder and my lifetime total operating surface and rotary (between centers) grinders is only 60-80 hours. I've always used whatever grinder my employer had, which was almost always older than me, and did just fine. Not splitting tenths, but holding them with some effort.

The parts we would use this for are similar to 4130 steel rings, 1/2" thick, OD 3-5", wall thickness 1/4" to 3/4", quantity ranges 5-100 and I would be happy at +/- 0.0001". We may just keep shipping them out, but other operations are coming in house and this would be the only one left.

My problem is that while I can tell you the difference between knee mills, I can't tell you the difference between grinders. I'm looking specifically at grinders with a power x,y,downfeed and coolant simply because past experience tells me those things make it a lot easier for a less experienced operator to get good parts off.

A new Kent/SuperTec/Acer 10x20 is going to run about 20k to my door, and a used one $10-12k, more if I want a permanent magnet chuck.
The smallest Okamoto I see with those features is a 12x24. Those seem to be closer to 30k used, and also weigh 1500 pounds more, which I doubt they did without reason.

I could get an old Chevalier on the local Craigslist for ~$1000+rigging, and if this going in my garage I would, but while we don't mind some maintenance and minor fixes, I need to know that this thing will work, so that isn't a good option.

In knee mill terms I don't want the green unmentionable, and probably not an M-head. A J or 2J Bridgeport with a power X would do nicely and a 5 axis VMC would be overkill.

Am I setting myself up for failure with the Kent? What do I gain with the Okamoto? Based on the prices above, am I way off on my estimates?
 
I use a 12x24 Okamoto almost daily, and have ran the same machine at other places. I really like them, but holding a tenth on a 24inch machine requires a bit of attention. not really difficult, just like in all grinding CLEANLINESS! My .02 cents.
 
Forgot to mention, I did run a Chevalier years ago, don`t remember much about it , but I do recall not liking it! So I guess thats .04 cents!!
 
4130 steel rings, 1/2" thick, OD 3-5", wall thickness 1/4" to 3/4",

Lots of 'air' in your grind on a reciprocating table... or any for that matter...some
grinding systems are just better suited to 'rings'...

consider a horizontal spindle rotary table or a vertical spindle rotary table.
Believe Okamoto makes a rotary table, and DCM has a vertical spindle.
Have a DCM on floor but typical tolerances for the parts sent there are like -.002.

I'd also say blanchard, but not sure about those tenths...
best o luck to you.
 
Lots of 'air' in your grind on a reciprocating table... or any for that matter...some
grinding systems are just better suited to 'rings'...

consider a horizontal spindle rotary table or a vertical spindle rotary table.
Believe Okamoto makes a rotary table, and DCM has a vertical spindle.
Have a DCM on floor but typical tolerances for the parts sent there are like -.002.

I'd also say blanchard, but not sure about those tenths...
best o luck to you.

Every now and then we have a protrusion to go around, so blanchard probably wouldn't go well, but horizontal spindle with a rotary table instead of a linear table is a new one to me, I'll have to look in to that, thank you. My thought with a typical linear surface grinder is that I could run a batch, but I'll have to think about the horizontal option. We do have an occasional protrusion in the center which would be much easier to avoid with a rotary device, assuming decent relief in the corner.
 
" Heald " and " Arter " made good " Ring Grinders " back in the day. Ring grinders usually have a rotating magnetic chuck and a reciprocating horizontal spindle. I've worked on several sizes but 15" , 24" and 40" chuck sizes are the most common. There are other makers in the field today but I'm not familiar with them. For ring type work they can't be beaten.

Regards Tyrone.
 
How well would a double disk grinder work?

Tom

We considered this one actually as that is how most of the parts are made in production. There are a few things stopping us:
1) A few of us know how to work a surface grinder, none of us have ever run a double disc grinder (might be simple, but we haven't done it).
2) Some of our parts have thing sticking up, so you have to grind, move it, then grind a different area. This is a cup grind in production.
3) A surface grinder would be useful for other odds and ends, less so with a double disc. I'm still thinking about the rotary table suggestion from above though.

A gerotor (inner and ring) would have been a better description of the parts, but either way, small round thing, usually flat, hole in the center.

Other than wasted cycle time are there any problems I should expect with the air space in the center? From the times I've made similar parts nothing comes to mind other than more deburring and needing to be careful about heat in small sections, but it wouldn't be the first time I learned something seemingly obvious about something I've been doing.
 
Make sure it's Kent and not Kent-USA totally different machines, two different manufacturer's.

Ironically Kent-USA being the offshore brand.

I didn't realize there were two, but looking in to it I think they might both be off shore. The logos among all of these are suspiciously similar, although the way they attach the controls looks slightly different. I wonder if this is more Clausing vs. Colchester or more Colchester vs. 600 Group?

There is the cream/red Kent USA who was very upfront that their grinders come from China (KGS-XXXX) and Taiwan (SGS-XXXX).
Automatic Feed Grinders

Then I found the blue/white Kent International/Kent USA, Inc., their home page shows a picture with the caption "Kent main factory in Taiwan"
KGS Surface Grinder / 3 Axes Automatic - KENT International USA
Appears to be exactly the same as this web page:
KENT International USA

I also found Kent Industrial, although that points to the two above.
Saddle Traveling Type - Automatic Series - KENT INDUSTRIAL CO., LTD.- Vertical Machining Center/Vertical CNC Machining Center/Surface Grinder/Double Column Vertical CNC Machining Center

I also found this thread, although the two companies listed here are both listed above, and both appear to be imports now.
https://www.practicalmachinist.com/...info-about-two-kent-grinder-companies-248880/
 
I'm a fan of " Okamoto " but that machine looks to have been repainted. I prefer to see machines in their original paint, even grinders.
The diamond holder appears to be missing from the wheel head dressing device.

Regards Tyrone.
 
You may want to sub out the work if it's a small orders. I agree on the Heald or Arter as well as a double disk grinder would work. A good Blanchard would work too. There is a company up here in MN that has Blanchards and double disk grinders. CNC Cylindrical & Precision Grinding Services | Thread, Centerless & Carbide Grinding Company | Minnesota Grinding Inc.
Initial set up would cost more then the grinding I bet. You would send them the rings they grind them and it's finished. I would send them say 200 rings and inventory them so when the customer calls they are in stock.

Arter and Healds are not in business any more. Lucas Precision still builds and rebuilds double disk grinders. J. L. Lucas Machinery Company, inc. | Or - Industrial Grinders | Centerless Grinders | Metalworking Machinery but go there to test run a used or rebuilt machine.

Kent factories are cousins who at one time owned the same company and they split up. 25 years ago Kent Grinders used Turcite on the ways and it would come loose, so unless you want to rebuild the machine then buy a newer less then 5 yrs old. Chevalier has used linear bearing ways for years. Good machine. Okamoto is a great machine and made in Japan. But as others have said. the regular H spindle reciprocating surface grinder will be slow and if it is a used machine I doubt you can hold .0001" or 2.
 
Plenty of local options if we want to sub it out, that's what we do now. Stocking at a supplier isn't an option as each part tends to be different (diameter, thickness, nuances of profile) than the ones before). Sadly, enough differences that keeping a "close enough" blank and doing the final operations when needed doesn't really work either (a future goal). Thought on bringing it in is that lead time goes down from our typical X weeks to "as soon as I can walk downstairs". A week or three time savings is significant.

Interesting about the Kent cousins. I wonder how often a family business is split like that and both halves survive? They seem to be mainly importers/onshore support, but there still might be something to be learned there.

I'll keep in mind the concerns on tolerance, it sounds like grinding a batch of blanks on whatever machine we decide to buy is a good idea.

Richard, are you saying holding a couple tenths would be hard overall (say one part on at a time, so a small area), or that holding that over the entire surface would be hard (ie a batch) due to uneven wear in the ways?
 
If these mystery objects you are grinding are round discs you've more chance of maintaining a tolerance with a good condition used ring grinder than on a conventional reciprocating table surface grinder.

Regards Tyrone.
 
My problem is that while I can tell you the difference between knee mills, I can't tell you the difference between grinders. I'm looking specifically at grinders with a power x,y,downfeed and coolant simply because past experience tells me those things make it a lot easier for a less experienced operator to get good parts off.

Am I setting myself up for failure with the Kent? What do I gain with the Okamoto? Based on the prices above, am I way off on my estimates?

The Kent grinders in the link posted above are comparable to the obsolete Okamoto 124N surface grinder.
The 12 X 24 Kent has a 7.5 HP spindle with P4 bearings. The bearing layout is not specified.
The Kent catalog does not reveal what design is used for the saddle ways. The table uses a V and flat way lined with Turcite.


The Okamoto has a 5 HP spindle with "Ultra Precision" bearings. This is the equivalent to a P2 or ABEC 9 specification.. Both the front and back spindle 2MM7210 angular contact bearing pairs are mounted face to face.
This was done to make each bearing pair less sensitive to misalignment. This design is limited to grinding spindles where bending stiffness is not a important factor in the machine design.
The Okamoto has a double V way saddle and a V and flat way for the table. Okamoto did not use a plastic lining for the ways.


The Okamoto uses a gravity fed way lubrication system that prevents the table from floating. The Kent catalog does not disclose what they use.
The Okamoto weighs 4900 lb and was made in Singapore.. The Kent weighs 4200 lb and is made in Taiwan or maybe China. The Okamoto appears to have more elaborate dust shields.

The ease of use, repeatable operation, and cost of maintenance are important concerns. The catalog descriptions provide no guidance in these areas.
The used price for a 124N with a magnetic chuck on Craigslist in California is $2000.

The ACC-DX version of the Okamoto 12X 24 has a micro processor controlled down feed ball screw design, double V ways on both the saddle and table and improved dust shields and splash guards. The spindle bearings are specified as P4.
The ask price seems to be in the $12,000 to 20,000 range on Ebay. The ask prices are not the selling prices of the grinders.

The used prices will vary depending on the number of hours on the spindle bearings, the presence of a over the wheel dresser, the dust/mist extraction system, the chuck design, the coolant filter, the number of wheel adapters supplied and the wear on the ways.
The spindle bearing life is about 5000 hours.

When you buy a new machine it will include a test report that lists measurements on spindle run out and X, Y, and Z axis alignment. There were eleven measurements made on the 124N and a additional grinding test that measured the parallel surface error on a plate that was ground on both sides. The report includes a tolerance and a actual measurement. The measurements are 1/2 to 1/8 the tolerances in the report I am looking at.

The manufacturers do not publish in their catalogs either the tolerance, the average measurement or the best machine measurement.
The problem is that one manufacturer might publish tolerances and another might publish their best results. A buyer would look at the numbers and conclude that the second manufacturer had a much better machine. That might not be true. A second problem is that if the buyer knew what the best numbers were he would refuse delivery of any machine that did not match the best numbers. The accuracy of a batch of machines will depend on the skill of the fitters and may vary significantly from one day to the next. The manufacturers solve the problem by not publishing any numbers at all.

That makes the comparison of the Okamoto and the Kent grinders very difficult unless the owner of the used machine still has the test report and the machine has not been abused.

If you are shopping for a a new machine it may be possible to receive the test report from the dealer in advance as a condition of the sale. In this case you are comparing specific machines and can make a decision based on the numbers.



Robert
 
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