View Full Version : Metal Lathes Metric sized Lathe Mandrels?..

Morey St. Denis
07-26-2011, 9:55 PM
Appreciate any suggestions on where I might source a standard tapered steel lathe mandrel of 10 mm diameter. That equates to 0.393" so is under the limit for any expanding mandrel gizmo usually beginning at 1/2" and up. Anticipating the standard ground turning mandrel taper of 0.0005" per inch, even a 13/32" fractional size mandrel (beginning at approximately 0.405" dia.) would be too large to accommodate my bore diameter of 0.393". Any 3/8" nominal sized mandrel at 0.375" would need to be an entirely impractical over 3 feet of length to get to 0.394" or 10mm. I've already contacted many of the usual domestic suppliers including: McMaster-Carr, Grainger, MSC, Travers, KBC, Victor, Taig, CDC, HHIP, etc, etc...

Looks like I'll be needing to contact an overseas supplier. Needing to rework several hubs made of sintered powdered metal (alloyed steel) with precision bore diameters of 10.0mm. Correct me if you know otherwise, but doesn't all the civilized world excepting the US, UK & Australia work to SI (System International) units (millimeters, etc.)? Precision lathe mandrels are a very common workholding tool for machine turning. Shouldn't be all that difficult?..

Bruce Page
07-26-2011, 10:11 PM
Don’t know what you’re trying to do but can’t you use compression instead of expansion, i.e. a precision 10 mm stud with nut?

Morey St. Denis
07-27-2011, 3:26 PM
Thanks Bruce, I rather suspect that you've taken me for a novice. So be it, I have been lurking & learning woodworking for four years instead of posting... No, the small steel hubs I need to turn must be faced on one end (perpendicular to the turning axis) all the way down almost to a root diameter of 10.2mm. Another option I can see to rework these parts in the correct manner would be to make up a fixture involving a steel base plate, bore a precision hole, press a shortened ~10.05 mm steel dowel pin, then surface grind using a magnetic workholding platen. I don't happen to have access to a parallel surface grinder... Furthrmore, I would then be faced with procuring two more metric dimensioned components; an oversized metric dowel pin, cutting it to length, and purchasing a slightly undersized 10.0 mm drill to assure the interference fit. A less desireable, but ultimately workable option might be to locate an 18mm metal lathe collet, but I suspect that's equally rare here in the US and precision lathe collets are far more expensive than a standard 4-5" length, precision ground mandrel with turning centers. My original thinking was that the cumulative expertise of all the accomplished craftsmen frequenting these forums might result in a lead for me as to where I might purchase some very common small accessory tooling for a lathe, but of German, Swiss, European, Japanese, Chinese, Malasian, etc, SI based manufacture.

ray hampton
07-27-2011, 3:39 PM
Morey, check this company web site for more info. LittleMachineShop.com
you never said what your lathe brand are but LMS sells parts for a majority of small lathes

Morey St. Denis
07-27-2011, 4:30 PM
Already been in contact with the sales dept. at "LittleMachineShop.com", it was implied under that "etc. etc." sorry about that, Ray. Most everything there appears in Ye Olde English fractional dimensions only. I'll likely being using a friend's compact metal lathe for this turning operation. Really would prefer getting a metric dimensioned standard taper mandrel turning on centers. One size fits any and all engine lathes.

All the cast metal, forged, heat-treated or pressed and sinter fabricated round symetrical parts you've ever come across having a central bore feature are reamed to the precision bore diameter then mounted on a mandrel to touch-up any radial features requiring closer toleraces. It's just the way it's done.. I just need to do it within accepted worldwide SI dimensions. 10.0 mm is a pretty common arbor size. Bet some of your more compact power tools may use the 10mm motor arbor size. 10 mm ID precision bearings are very common.


ray hampton
07-27-2011, 4:39 PM
Morey, will you tell me the name of your lathe and maybe I will be able to help more , you can send me a P M if you prefer

ray hampton
07-27-2011, 4:47 PM
are the taper mandrel that you need close to the size of a number 0 morse taper

Morey St. Denis
07-27-2011, 5:34 PM
No, turning mandrels use a standard taper of about 0.0005" of diameter per lineal inch and the small end typically starts about 0.001" under the specified nominal diameter. The Morse taper is relatively more agressive (intended for an entirely different purpose) Don't recall exactly without consulting my "Mark's" guide to engineering or "Machineries Handbook", but I'd guess the Morse Taper standard is more in the range of 1/16" per inch.

Jerry Bruette
07-27-2011, 5:57 PM
I worked in a factory for a while that made oil pumps for automobile engines. The gears for the pumps were made from a sintered material and were faced using a mandrel as you state. Only difference is the mandrel we used was expandible, it had a bladder inside that was inflated using air and pushed metal pads out to engage the bore of the gears.

I have no idea if the mandrel was custom made or maybe even made in house by the tool and die department. But it worked great and was fast. Maybe you could make your own expanding mandrel.


Wes Grass
07-27-2011, 6:33 PM
Hardinge will be happy to sell you an 18mm 5C collet for about $30. Or you could buy an 'emergency' collet and bore it to fit. But, ironically, they cost more. An expanding collet would be a better way of fixturing this, but the price of that will be significantly higher.

A split bar with an expanding screw could work. Been done many times before.

Edit, to add:


Available as an expanding mandrel, if you prefer.

Morey St. Denis
07-28-2011, 7:12 PM
Thanks for that info. The Hardinge expanding arbor #5C-100S does indeed claim to accommodate 1/8" to 1/2" nominal diameters with expansion to +0.015", but that's one expensive turn-it-yourself workholding tool! Considering the cost, specialized machinery and effort required to turn and surface that raw "soft" tool to 10mm, I'm confident it would be far more practical and afford better precision to just turn a simple tapered mandrel exactly to size from 7/16" rod stock! The clever solution would be to indentify an international supplier of metric tooling. Few seem to grasp the notion that the US remains the only place where fractional English dimensioning is still actively employed.

Seems to me that a step in the right direction might be a suggestion for a hobby machinist forum with international contributors. Leveraging on the fact that our English language remains a highly accepted form of international business communication, if not our awkward dimensional system... A compact Par Avion parcel in the range of 100 grams would cost a fraction of the aforementioned US sourced complex specialty tooling.

Has anyone ever tried some 9 or 10 thousandths brass or aluminum shim material over a small precision ground mandrel such as the readily available 3/8"?..


Gerald Wubs
07-30-2011, 2:20 AM
Hi Morey,
I too am a fan of Metric, but I know that Imperial is here to stay in North America for the near future anyway. I know what you are after, and why, but I don't have an answer for you as to where to get the mandrel you are after. My advice is too have one made. Any competent shop with cylindrical grinding capabilities should be able to make a mandrel with a taper of .0005" per foot or there abouts? The actual taper does not matter greatlly, that is .0004 or .0006" / ft . would likely be OK? I have attended the AGMA Gear School in Chicago Ill. so I do know about precision mandrels. Just grind a taper on dead centers of nearly .0005"/ in.

Gerald Wubs
07-30-2011, 2:25 AM
My above post should read .00005"/in not ft Sorry:)

Gerald Wubs
07-30-2011, 2:28 AM
0005"/in final answer - that's what I get for posting after my bedtime:rolleyes: