Router Cutter Bearing Screws

UKworkshop.co.uk

Help Support UKworkshop.co.uk:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

niall Y

Established Member
Joined
1 Nov 2018
Messages
1,220
Reaction score
960
Location
CARDIGAN
Here is what should be a fairly simple question. - What size are the screws used to hold the bottom bearings on router cutters? One has just broken off in a cutter, which I have, luckily , managed to remove the stump of. Now I need a replacement It seems to be measure a tad under 3mm diameter. so I am assuming it to be metric. None of the ones off my old cutters seems to fit so again I am making the assumption that these are imperial. But , of course I could be wrong.
 
You have not mentioned the cutter diameter. If is a metric dimension then it is likely the bearing screw is an ISO M3.
The diameter of this screw thread will be around 2.95 mm and the pitch of the thread will be 0,5 mm. Good luck with your search.
 
Giving this an educated guess that it depends on the cutter - eg 1/4”. 1/2 “ etc . I’d imagine the bigger the cutter the bigger the bearing/ screw - also maybe different manufacturers would use different screws.. I’d try using an appropriate size screw and try it for size , be aware the pitch could be different. Some of the better router manufacturers will give you the dimensions for there cutters including the bearing/ screw sizes .
 
What type of head is on the broken screw? If it needs an allen key, you could make a reasonable inference on the language of the screw from the key (imperial or metric) that turns it.

If it is hexagon head, try both your imperial and metric adjustable spanners on it to see which best suits.
 
Thanks for the input so far folks. And, in response, I feel I should add a bit more information about the cutter. It is a cheap Chinese 1/2" straight cutter, and it looks to be a standard Allen screw in the bottom bearing.

I've just taken a punt and ordered some 3mm Allen screws, in that - I won't be much out of pocket if they don't fit. And, if they don't fit............. well this is where the problems might begin. 1/8" Whitworth would be my next try, but after this -?? I do have some thread gauges so I will check if any of these fit. I suspect I will need a lot of magnification to help me, as the eyes aren't as good as they used to be.:unsure:

The answer could be - Just buy another cheap cutter. Except, I'm not using it as a router cutter but as a long reamer, as in the attached picture. and I don't particularly relish the idea of having to reattach a new one to the shaft, if I don't have to. :)
 

Attachments

  • IMG_3819_1 RO.jpg
    IMG_3819_1 RO.jpg
    1 MB · Views: 0
Following on from my original question the M3 Allen screws arrived in the post today, I tried one out for fit and it went in part way. I used a 3mm tap to recut the hole thread and it then went in all the way . This will suit me just fine as I am not using the cutter in a router, so no chance of any bearing flying off.😲

Judging by this I couldn't quite be sure that the original was M3, but I tried one of my new screws in one of my more recent router cutters, and it went in without any problem. As I had previously borrowed the screw from this particular cutter to try and see if it fitted the broken one ,( and found that it did), I have to conclude that the original thread is in fact 3mm, 0.50

On a similar tack - I have been looking up Torx screws for holding carbide tips on some of my indexable lathe tools, with a view to getting a few spares. And , I note that these are also Metric coarse. with some of them being offered in the in-between half sizes as well..
 
On a similar tack - I have been looking up Torx screws for holding carbide tips on some of my indexable lathe tools, with a view to getting a few spares. And , I note that these are also Metric coarse. with some of them being offered in the in-between half sizes as well..
The shape - or 'Type' - of drive socket on screws has no bearing upon the thread!

You could quite easily have a BA thread Set Screw ( or Whitworth, Unified etc.) with a Hex (Allen), Square (Robertson), Torx, PoziDriv, Tri Wing - - - - or any of many more 'sockets', just as you could have any number of different 'Head' types; Button, Countersunk, Flanged, Cap.

Also the 'Metric' Standard (ISO) only has "½ sizes" between 2 & 6mm.

What I'm saying is, don't get hung up on thinking that the type of screw and the thread thereon having any relationship.
 
The shape - or 'Type' - of drive socket on screws has no bearing upon the thread!

You could quite easily have a BA thread Set Screw ( or Whitworth, Unified etc.) with a Hex (Allen), Square (Robertson), Torx, PoziDriv, Tri Wing - - - - or any of many more 'sockets', just as you could have any number of different 'Head' types; Button, Countersunk, Flanged, Cap.

Also the 'Metric' Standard (ISO) only has "½ sizes" between 2 & 6mm.

What I'm saying is, don't get hung up on thinking that the type of screw and the thread thereon having any relationship.
Thanks for taking the time to reply. However, having just reread what I wrote I fear you have gone off at a bit of a tangent, by misinterpreting what I said. :)

I was interested in your comments on the Metric Standard regarding the half sizes. I have to admit that this isn't something I have come across before, but it tallies with the range of sizes being offered to hold down carbide tips in lathe tooling
 
Thanks for the link. I've been through a lot of these on Ebay. And they all seem remarkably coy about what the actual thread size of their screws is. I think I have come to the conclusion that they are most likely to be M3.

Whiteside cutters list the three sizes of their screws as 3-30, 5-40 and 10-32, Which I understand to be UNC, 0.099" - 40TPI, 0.125"- 40TPI and 0.190m- 32TPI, respectively.

Edit - from Whitehill to Whiteside, also 3- 30 should in fact read 3-48 ( well spotted @J-G )
 
Last edited:
Whitehill cutters list the three sizes of their screws as 3-30, 5-40 and 10-32, Which I understand to be UNC, 0.099" - 40TPI, 0.125"- 40TPI and 0.190m- 32TPI, respectively
Only one of those is 'UNC', Nº5 x 40.

Nº10 x 32 might fall into the UNEF series but is not in any table I am aware of, I would therefore class it as UNS (Unified Special).

Nº3 UNC would be 48tpi, UNF, 56tpi. - - - 40 tpi would again be a 'special' but 30tpi (as initially quoted) is unlikely to be achivable in any viable length since the core Ø would be <0.06".
 
Only one of those is 'UNC', Nº5 x 40.

Nº10 x 32 might fall into the UNEF series but is not in any table I am aware of, I would therefore class it as UNS (Unified Special).

Nº3 UNC would be 48tpi, UNF, 56tpi. - - - 40 tpi would again be a 'special' but 30tpi (as initially quoted) is unlikely to be achivable in any viable length since the core Ø would be <0.06".
Well spotted that man.......... I noted the size down wrongly. The smaller one is in fact 3-48. And from the charts I've just looked at 10-32 seems to be UNF.
 
And from the charts I've just looked at 10-32 seems to be UNF.
Nº10 UNF would be 28tpi - there is no UNF dia. at 32tpi.

UNEF starts at Nº12 x 32 ie. Nº0 to Nº10 are undefined - but there are also Unified constant pitch series.
 
Nº10 UNF would be 28tpi - there is no UNF dia. at 32tpi.

UNEF starts at Nº12 x 32 ie. Nº0 to Nº10 are undefined - but there are also Unified constant pitch series.
Try searching journeymans-workshop.uk/unified.php
 
Try searching journeymans-workshop.uk/unified.php
D'OH!!! - at least you've found and error in my Thread measuring program!

Although that .PHP file is correct, I normally work from the 'standard' - My program uses a transcription from the standard and I had simply made an error in the Unified listing :oops: - - - now corrected
 
Last edited:
Back
Top