Mitsubishi Boring Bars

G'day. I am thinking of purchasing some of these **LINK** for boring some small holes accurately (typically small model engine cylinders) prior to lapping the bore.

I know that they are a tad expensive but cost is not a problem if they work well and last a while.

So does anybody have any experience and/or tips for using these tools?

* Danny M *

Danny, any particular one you are looking at ? solid or insert and if insert what sort of shape.

I tend to take most of it out with a similar insert bar that takes the CCMT (SCLCR holder)tip but find that if sneaking up on the diameter that HSS is better for the last few passes, I feel that not having the radius tip of the inserts the bar gets deflexted less so you get a more parallel bore which takes less effort to lap. This applies to both steel liners for glow and diesel as well as larger Cast Iron liners on spark ignition 2-strokes as well as hit & miss engines.

For boring the ali castings or solid to put the liner in then I always use insert tooling with the CCGT tips for non ferrous.

Edited By JasonB on 06/01/2017 12:01:10

The Dimple bars work great. I have a few and think they are great. I use these inserts in the ones I have. CCGT060202MP-CK PR1425 These inserts are by Kyocera but fit the Dimple bar really well. I have the 10mm shank dimple bar , and the 8mm shank bar, that both take 6mm series insert. These have a small 0.2mm nose radius and are very positive and sharp cutting geometry. Will cut all material, even ball bearing race ways. I also brought an external holder to use these same inserts for OD turning.

The only other option I think for boring bars are the vibration dampened bars from people like Sumitomo Corp, and others. They have a Carbide weight that floats around near the head of the boring bar, and cancels out a lot of the vibration, but they are quite pricey. The moving weight type are also made by Kennametal ,and Sandvik, or used to be anyway.

Neil

Danny

There must be 40 different boring bars shown in your link so its not obvious which ones or types you are considering. I use the same technique and boring bar type as Jason.

No idea what Neil's 'dimple' bars are but they sound interesting.

Ian P

It depends what size you want to go down to, Iscar do some very nice small tooling in their Picco range and their small insert RH and LH boring/threading bars MGSIR/L are available in 6mm and 8mm, for bores of 8mm and up the Cham-Groove tooling has a wide range of tip profiles for boring, grooving, back-boring and threading with MGCH bars accepting both left-hand and right-hand tips.

- Nick

Not familiar with the Mitsubishi Dimple bars but they sound interesting. As well as being solid carbide (stiff), it seems the scalloped shape of the end of the bar is claimed to reduce vibrations and clear swarf - "by reducing the weight of the head, the damping properties are improved".

They take industry standard inserts.

Murray

That's them Muzzer, I have them at work also, but in the larger sizes. The through coolant of commercial machines is nice, but at the same time, don't want to be showered in coolant at home. In the smaller sizes I like the CC style inserts, in the larger I like the DC style inserts and the TN style for roughing in the larger bars, ie the 32mm and 40mm shank bars.For Home I have the small ss inserts, the TNMG16 as a std oiuter turn tool, and the DCMT11T3 inserts for outer turning as well. For jobs where the work piece is like a bell and sings, then I like to use in those cases the tools with the active vibration dampening, ie the ones with a floating weight. Regular steel bodied tools can be dampened by drilling a hole and fitting a loose piece of carbide in the hole. So a 5mm hoe is about right for a piece of Ø3/16 carbide piece. The carbide slug wants to be big enough that when it vibrates it makes the bar sound dead instead of ringing. For boring bars, I make the hole no more than 50% of the area of the boring bar, and plug it with a brass plug. This can also be done to external tools as well, and is good when you have tools sticking out a long way, and a work piece that is likely to be vibrating itself. Work piece harmonics and cutting tool harmonics is an interesting subject all on it's own. Neil

I am contemplating the Micro-Mini Twin, 03RS and 05RS from this catalogue **LINK**

The Micro-Dex C04 SCLC with GSCLCR03 inserts are also tempting.

Apart from internal boring of small cast iron pistons I also have a requirement to bore small steel cylinders/liners as small as 6mm diameter.

The surface finish claimed for these tools should reduce lapping to a minimum.

Regards * Danny M *

Edited By Danny M2Z on 06/01/2017 22:08:12

Interesting, Danny. Do you have any idea of the price?

Roger

Roger, I did say that they were not exactly cheap. Only prices that I could pin down are in the U.S. **LINK** but for the jobs that I envisage they would be quite invaluable so prepared to pay the price and hope that I don't bust one in a hurry.

Compared to all the time saved faffing about (I have ground similar boring tools from HSS) making my own so might be worth a punt.

This one was ground from 1/8" sq HSS to bore a Cox Pee Wee .020 cylinder head for a contra-piston - it worked!

* Danny M *

I buy what I can as making things takes time. Not retired, I would rather just buy and use it. I only make special tools that are not available, like a threading tool to cut M5X 0.5 pitch thread that goes into a 45 deg cone, it is only 0.4 mm wide at the business end.

Neil

Here is the micro threader, Great work there Danny.

.

Thanks for the link, Danny ... They do look rather good

I do, however, find this little warning note [whilst perfectly reasonable] rather scary:

... It's a very fine line between reaching "the center line of a workpiece" and crossing it.

As illustrated; one gives a perfect hemisphere, and the other a ruined tool and maybe a ruined job.

MichaelG.

I do, however, find this little warning note [whilst perfectly reasonable] rather scary:

... It's a very fine line between reaching "the center line of a workpiece" and crossing it.

As illustrated; one gives a perfect hemisphere, and the other a ruined tool and maybe a ruined job.

MichaelG.

I carry out bowl cutting frequently for some parts I make in aluminium. First op is to use a 6mm ball end mill to drill to exact depth of bowl required. 2nd op with a 6mm boring tool roughs out and finishes the bowl to the depth and radius required, for the finish pass the tool starts cutting from the centre so avoiding damage to the tip by upward moving metal.

Emgee

Danny

You might also have a look at Micro 100 small carbide boring tools.

Catalogue: http://www.micro100.com/catalogs.htm

Quite a few on eBay USA, some of which may be suitable for you. Not sure how the price compares to Mitsubishi, though.

Dave
The Emerald Isle

Noted, emgee ... But my comment was specific to the very small carbide tool referenced by Danny.

MichaelG.

Edited By Michael Gilligan on 07/01/2017 11:55:22

Michael, I have found the same applies to any size finely ground carbide tooling, solid or insert are both likely to chip on the cutting edge with even light reversed cutting forces as would be the case by going beyond the centre of the bowl shown.

Emgee

Emgee,

Thanks ... Yes, I am aware of that ^^^

I hoped I had made that much obvious, by writing: "[whilst perfectly reasonable]"

The thing I found 'scary' is how fine the dividing line between success and failure might be, on these particular very small and not inexpensive boring bars.

I won't labour it any further.

MichaelG.

Mike G, The same applies to any turning tool that is rubbed from the reverse. It is worse on a inner sphere as described, you have the work piece acting as a lap over the cutting edge. The above refers to only a solid turned sphere. If there is a small hole or if the bottom of the sphere is formed some other way it is ok. The problem with any small tools is the very centre of any part. As it has zero surface speed, it can only be removed by deformation or by the chisel effect. Very small tools are just not that strong in their geometry and by their nature are weak. That makes them very susceptible to centre line height setting. Often when boring having the tool slightly above centre height is an advantage as the loading of the tool, then deflects down and in doing so reduces very slightly the cutting load. When the tool is exactly on centre line, when it deflects down, it will take a very slightly bigger cut. When it is set below centre line, it will have the tendency to be digging in and taking cuts big enough to either damage the tool, or leave a very poor surface finish. So with small tools, the more rigid the material the tool is and the lighter cuts makes for the tool lasting a long time with good surface finish. Cutting fluids that promote the shearing of the material, ie reduce cutting forces, help a lot as well. On small stuff, I keep the corner radius to less than 0.2mm or 8thou. On micro bars, less than Ø3mm diameter, I have the tool radius at 0.1mm or 4 thou. This allows at a 1 thou per rev feedrate to get accptable surface finishes. If I need a very good finish, I hand feed at about the 0.01mm per rate approx. So when the spindle is doing 600 rpm, I feed the main hand wheel so that I do 1/4 turn every 7 seconds, or 1 rev in 30 seconds. This is for the 0.1mm nose radius tool. With .2mm radius tool it is turning the hand wheel 1 rev per 15 seconds, or 4 revs per minute. The myford box does not allow 0.001 inches per rev feed rate. It takes time to learn to turn a handle at a feedrate, but is really worth while to learn.

Neil,

Thank you for taking the trouble to describe your working method.

... Regarding the first part of your post, however; I can only refer back to my reply to emgee.

MichaelG.

P.S. ... I do much prefer to be called Michael.