By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Forum House Ad Zone

Centre punch size

All Topics | Latest Posts

Search for:  in Thread Title in  
Wolfie25/09/2011 18:16:43
avatar
502 forum posts
OK silly question alert!
 
I want to buy a small centre punch at an online supplier. Thing is they are given in sizes ranging fron below 1/8" to over 1/4".
 
What I want to know is what that measurement is? Is it the tip or what??
JasonB25/09/2011 19:11:53
avatar
25215 forum posts
3105 photos
1 articles
I would say its measured at the top of the 90deg cone before the long taper starts so the 1/8" one would be fine for small work.
 
Edit if this is for your bit of 3/16 bar or any accurate work  then you should use a dot punch first as this makes it easier to shift the mark if you don't get it spot on the first time. Once happy with teh dot punch hark follow it up with a centre punch
 
Even then I now tend to use the DRO rather than mark out if it needs to be precise but its still good to learn the basics while saving up for a DRO.
 
J

Edited By JasonB on 25/09/2011 19:40:58

Wolfie25/09/2011 21:37:54
avatar
502 forum posts
DRO??
 
And whats a dot punch?
Stub Mandrel25/09/2011 21:44:36
avatar
4318 forum posts
291 photos
1 articles
Dot punch is like a finer, more pointed centre punch. Give it a light tap to make an accurate dot, then you can put the centre punch in the dot and give it a (little) more welly.
 
Neil
JasonB25/09/2011 21:47:40
avatar
25215 forum posts
3105 photos
1 articles
Dot punch looks just like a centre punch but is more pointed - 60deg included angle vs 90deg. The point engages into the scriber lines better and as I said above can be pulled over by tilting slightly and hitting again if its not right first tile. Also gives a better hole for divider points to engage into.
 
DRO Digital Read Out, use it on teh mill to vet very accurate hole positions.

Edited By JasonB on 25/09/2011 21:48:45

DMB25/09/2011 22:03:52
1585 forum posts
1 photos
Wolfie,
Like JasonB said,dot punch lightly first, check its spot on then use centre punch with a slightly heavier bump with a small hammer. Note, you dont need to hit it hard and create a huge bomb crator and when using the dot punch, if its not exactly where it should be, lean punch over at an angle, pointing in the direction that the punch mark needs to be moved and give it a very light tap, check re-positioning OK then hold upright and give it a harder tap.
John.
Terryd25/09/2011 22:11:06
avatar
1946 forum posts
179 photos
Hi Wolfie,
 
A DRO is a Digital Read Out . These are digital scales fixed to some machines to show the accurate position of the tools or work. Typically a lathe will have one for saddle travel and one for cross slide. ( occasionally one for topslide) a Milling machine usually has one each for the X, Y and Z axes.
 
A 'dot' punch is a fine punch with a sharp angle (60 degrees included) point for accurately marking centres. A 'centre' punch has a more robust point with an included angle of around 120 degree included angle (about the same as a drill angle of 118 degrees) this gives the drill point a good location.
 
It is normal practice to use a dot punch first to lightly mark a centre (using a magnifying glass and light is preferable) and if accurate this is followed with a 'centre' punch to give a larger mark for the pilot drill to locate. If not accurate the light dot punch mark can be moved by tapping the punch at an angle in the direction it needs to be moved before finishing with a centre punch.
 
I make my own punches using some high carbon steel I have but they can be easily made from silver steel. PM me if you need advice and are interested. Here is an example made from some salvaged silver steel The bottom one is the home made punch. It too about 20 minutes from start to using:
 

 
In the past a dot punch would also be used to mark cutting lines on an an irregular piece or component and you would cut and file until you 'halved' the dot marks and then remove the half marks by chamfering the edges of the work.
 
Hope this helps, us old timers take too much for granted. If you need any more advice don't be afraid to ask.
 
Best regards,
 
Terry
Ian S C26/09/2011 10:53:19
avatar
7468 forum posts
230 photos
I find that the little dot punchs that I make out of old chainsaw files are very handy for small work. The files I use are 3/16"- 5mm and 1/4"- 6mm , I seem to find worn out files turning up quite often.
At school metalwork classes, our teacher got us to dot punch the lines to file to, and he inspected all our work, and expedted to see half the dot. Ian S C

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Sign up to our Newsletter

Sign up to our newsletter and get a free digital issue.

You can unsubscribe at anytime. View our privacy policy at www.mortons.co.uk/privacy

Latest Forum Posts
Support Our Partners
cowells
Sarik
MERIDIENNE EXHIBITIONS LTD
Shopping Partners
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest

 

Donate

donate